Linked Data Platform (LDP) defines a set of rules for HTTP operations on web resources, some based on RDF, to provide an architecture for read-write Linked Data on the web.
Status of This DocumentThis section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.
This document has been reviewed by W3C Members, by software developers, and by other W3C groups and interested parties, and is endorsed by the Director as a W3C Recommendation. It is a stable document and may be used as reference material or cited from another document. W3C's role in making the Recommendation is to draw attention to the specification and to promote its widespread deployment. This enhances the functionality and interoperability of the Web.
Please see the Working Group's implementation report.
This W3C Recommendation was published by the Linked Data Platform Working Group. Discussions of this document are on public-ldp-comments@w3.org (subscribe, archives).
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This document is governed by the 14 October 2005 W3C Process Document.
Table of Contents 1. IntroductionThis section is non-normative.
This specification describes the use of HTTP for accessing, updating, creating and deleting resources from servers that expose their resources as Linked Data. It provides clarifications and extensions of the rules of Linked Data [LINKED-DATA]:
This specification discusses standard HTTP and RDF techniques used when constructing clients and servers that create, read, and write Linked Data Platform Resources. LDP Primer provides an entry-level introduction with many examples in the context of a fictional application. LDP Best Practices and Guidelines discusses best practices that you should use, and anti-patterns you should avoid, when constructing these clients and servers.
This specification defines a special type of Linked Data Platform Resource: a Container. Containers are very useful in building application models involving collections of resources, often homogeneous ones. For example, universities offer a collection of classes and a collection of faculty members, each faculty member teaches a collection of courses, and so on. This specification discusses how to work with containers. Resources can be added to containers using standard HTTP operations like POST (see section 5.2.3 HTTP POST).
The intention of this specification is to enable additional rules and layered groupings of rules as additional specifications. The scope is intentionally narrow to provide a set of key rules for reading and writing Linked Data that most, if not all, other specifications will depend upon and implementations will support.
This specification provides some approaches to deal with large resources. An extension to this specification provides the ability to break large resource representations into multiple paged responses [LDP-PAGING].
For context and background, it could be useful to read Linked Data Platform Use Case and Requirements [LDP-UCR] and section 6. Notable information from normative references.
2. TerminologyTerminology is based on W3C's Architecture of the World Wide Web [WEBARCH] and Hyper-text Transfer Protocol ([RFC7230], [RFC7231], [RFC7232]).
The terms "client" and "server" refer only to the roles that these programs perform for a particular connection. The same program might act as a client on some connections and a server on others.
HTTP enables the use of intermediaries to satisfy requests through a chain of connections. There are three common forms of HTTP intermediary: proxy, gateway, and tunnel. In some cases, a single intermediary might act as an origin server, proxy, gateway, or tunnel, switching behavior based on the nature of each request. [RFC7230].
ldp:member and dcterms:isPartOf are representative examples.
Each linked container exposes properties (see section 5.2.1 General) that allow clients to determine which pattern it uses, what the actual membership-predicate and membership-constant-URI values are, and (for containers that allow the creation of new members) what value is used for the member-derived-URI based on the client's input to the creation process.
The namespace for LDP is http://www.w3.org/ns/ldp#.
Sample resource representations are provided in text/turtle format [turtle].
Commonly used namespace prefixes:
@prefix dcterms: <http://purl.org/dc/terms/>. @prefix foaf: <http://xmlns.com/foaf/0.1/>. @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>. @prefix ldp: <http://www.w3.org/ns/ldp#>. @prefix xsd: <http://www.w3.org/2001/XMLSchema#>.3. Conformance
As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.
The key words MAY, MUST, MUST NOT, RECOMMENDED, SHOULD, and SHOULD NOT are to be interpreted as described in [RFC2119].
The status of the sections of Linked Data Platform 1.0 (this document) is as follows:
A conforming LDP client is a conforming HTTP client [RFC7230] that follows the rules defined by LDP in section 4. Linked Data Platform Resources and also section 5. Linked Data Platform Containers.
A conforming LDP server is a conforming HTTP server [RFC7230] that follows the rules defined by LDP in section 4. Linked Data Platform Resources when it is serving LDPRs, and also section 5. Linked Data Platform Containers when it is serving LDPCs. LDP does not constrain its behavior when serving other HTTP resources.
4. Linked Data Platform Resources 4.1 IntroductionThis section is non-normative.
Linked Data Platform Resources (LDPRs) are HTTP resources that conform to the simple patterns and conventions in this section. HTTP requests to access, modify, create or delete LDPRs are accepted and processed by LDP servers. Most LDPRs are domain-specific resources that contain data for an entity in some domain, which could be commercial, governmental, scientific, religious, or other.
Some of the rules defined in this document provide clarification and refinement of the base Linked Data rules [LINKED-DATA]; others address additional needs.
The rules for Linked Data Platform Resources address basic questions such as:
Additional non-normative guidance is available in the LDP Best Practices and Guidelines that addresses questions such as:
The following sections define the conformance rules for LDP servers when serving LDPRs.
LDP-RS's representations may be too big, one strategy is to break up the response representation into client consumable chunks called pages. A separate LDP specification outlines the conformance rules around pagination [LDP-PAGING].
A LDP server can manage two kinds of LDPRs, those resources whose state is represented using RDF (LDP-RS) and those using other formats (LDP-NR). LDP-RSs have the unique quality that their representation is based on RDF, which addresses a number of use cases from web metadata, open data models, machine processable information, and automated processing by software agents [rdf11-concepts]. LDP-NRs are almost anything on the Web today: images, HTML pages, word processing documents, spreadsheets, etc. and LDP-RSs hold metadata associated with LDP-NRs in some cases.
Fig. 1 Samples of different types of LDPRsThe LDP-NRs and LDP-RSs are simply sub-types of LDPRs, as illustrated in Fig. 2 Class relationship of types of Linked Data Platform Resources.
Fig. 2 Class relationship of types of Linked Data Platform Resources 4.2 Resource 4.2.1 General 4.2.1.1 LDP servers MUST at least be HTTP/1.1 conformant servers [RFC7230]. 4.2.1.2 LDP servers MAY host a mixture of LDP-RSs and LDP-NRs. For example, it is common for LDP servers to need to host binary or text resources that do not have useful RDF representations. 4.2.1.3 LDP server responses MUST use entity tags (either weak or strong ones) as responseETag header values, for responses that contain resource representations or successful responses to HTTP HEAD requests. 4.2.1.4 LDP servers exposing LDPRs MUST advertise their LDP support by exposing a HTTP Link header with a target URI of http://www.w3.org/ns/ldp#Resource, and a link relation type of type (that is, rel="type") in all responses to requests made to an LDPR's HTTP Request-URI [RFC5988].
4.2.1.5 LDP servers MUST assign the default base-URI for [RFC3987] relative-URI resolution to be the HTTPNote: The HTTP
Linkheader is the method by which servers assert their support for the LDP specification on a specific resource in a way that clients can inspect dynamically at run-time. This is not equivalent to the presence of a (subject-URI,rdf:type,ldp:Resource) triple in an LDP-RS. The presence of the header asserts that the server complies with the LDP specification's constraints on HTTP interactions with LDPRs, that is it asserts that the resource has Etags, supports OPTIONS, and so on, which is not true of all Web resources.Note: A LDP server can host a mixture of LDP-RSs and LDP-NRs, and therefore there is no implication that LDP support advertised on one HTTP
Request-URImeans that other resources on the same server are also LDPRs. Each HTTPRequest-URIneeds to be individually inspected, in the absence of outside information.
Request-URI when the resource already exists, and to the URI of the created resource when the request results in the creation of a new resource. 4.2.1.6 LDP servers MUST publish any constraints on LDP clients’ ability to create or update LDPRs, by adding a Link header with an appropriate context URI, a link relation of http://www.w3.org/ns/ldp#constrainedBy, and a target URI identifying a set of constraints [RFC5988], to all responses to requests that fail due to violation of those constraints. For example, a server that refuses resource creation requests via HTTP PUT, POST, or PATCH would return this Link header on its 4xx responses to such requests. The same Link header MAY be provided on other responses. LDP neither defines nor constrains the representation of the link's target resource. Natural language constraint documents are therefore permitted, although machine-readable ones facilitate better client interactions. The appropriate context URI can vary based on the request's semantics and method; unless the response is otherwise constrained, the default (the effective request URI) SHOULD be used. 4.2.2 HTTP GET 4.2.2.1 LDP servers MUST support the HTTP GET method for LDPRs. 4.2.2.2 LDP servers MUST support the HTTP response headers defined in section 4.2.8 HTTP OPTIONS for the HTTP GET method. 4.2.3 HTTP POST
Per [RFC7231], this HTTP method is optional and this specification does not require LDP servers to support it. When a LDP server supports this method, this specification imposes no new requirements for LDPRs.
Clients can create LDPRs via POST (section 5.2.3 HTTP POST) to a LDPC, via PUT (section 4.2.4 HTTP PUT), or any other methods allowed for HTTP resources. Any server-imposed constraints on LDPR creation or update must be advertised to clients.
Per [RFC7231], this HTTP method is optional and this specification does not require LDP servers to support it. When a LDP server supports this method, this specification imposes the following new requirements for LDPRs.
Any server-imposed constraints on LDPR creation or update must be advertised to clients.
4.2.4.1 If a HTTPPUT is accepted on an existing resource, LDP servers MUST replace the entire persistent state of the identified resource with the entity representation in the body of the request. LDP servers MAY ignore LDP-server-managed properties, and MAY ignore other properties such as dcterms:modified and dcterms:creator if they are handled specially by the server (for example, if the server overrides the value or supplies a default value). Any LDP servers that wish to support a more sophisticated merge of data provided by the client with existing state stored on the server for a resource MUST use HTTP PATCH, not HTTP PUT. 4.2.4.2 LDP servers SHOULD allow clients to update resources without requiring detailed knowledge of server-specific constraints. This is a consequence of the requirement to enable simple creation and modification of LDPRs. 4.2.4.3 If an otherwise valid HTTP PUT request is received that attempts to change properties the server does not allow clients to modify, LDP servers MUST fail the request by responding with a 4xx range status code (typically 409 Conflict). LDP servers SHOULD provide a corresponding response body containing information about which properties could not be persisted. The format of the 4xx response body is not constrained by LDP.
Non-normative note: Clients might provide properties equivalent to those already in the resource's state, e.g. as part of a GET/update representation/PUT sequence, and those PUT requests are intended to work as long as the LDP-server-managed properties are identical on the GET response and the subsequent PUT request. This is in contrast to other cases like write-once properties that the server does not allow clients to modify once set; properties like this are under client and/or server control but are not constrained by LDP, so they are not LDP-server-managed triples.4.2.4.4 If an otherwise valid HTTP
PUT request is received that contains properties the server chooses not to persist, e.g. unknown content, LDP servers MUST respond with an appropriate 4xx range status code [RFC7231]. LDP servers SHOULD provide a corresponding response body containing information about which properties could not be persisted. The format of the 4xx response body is not constrained by LDP. LDP servers expose these application-specific constraints as described in section 4.2.1 General. 4.2.4.5 LDP clients SHOULD use the HTTP If-Match header and HTTP ETags to ensure it isn’t modifying a resource that has changed since the client last retrieved its representation. LDP servers SHOULD require the HTTP If-Match header and HTTP ETags to detect collisions. LDP servers MUST respond with status code 412 (Condition Failed) if ETags fail to match when there are no other errors with the request [RFC7232]. LDP servers that require conditional requests MUST respond with status code 428 (Precondition Required) when the absence of a precondition is the only reason for rejecting the request [RFC6585]. 4.2.4.6 LDP servers MAY choose to allow the creation of new resources using HTTP PUT. 4.2.5 HTTP DELETE
Per [RFC7231], this HTTP method is optional and this specification does not require LDP servers to support it. When a LDP server supports this method, this specification imposes no new blanket requirements for LDPRs.
Additional requirements on HTTP DELETE for LDPRs within containers can be found in section 5.2.5 HTTP DELETE.
Note that certain LDP mechanisms rely on HTTP headers, and HTTP generally requires that HEAD responses include the same headers as GET responses. Thus, implementers should also carefully read sections 4.2.2 HTTP GET and 4.2.8 HTTP OPTIONS.
HEAD method. 4.2.7 HTTP PATCH
Per [RFC5789], this HTTP method is optional and this specification does not require LDP servers to support it. When a LDP server supports this method, this specification imposes the following new requirements for LDPRs.
Any server-imposed constraints on LDPR creation or update must be advertised to clients.
4.2.7.1 LDP servers that supportPATCH MUST include an Accept-Patch HTTP response header [RFC5789] on HTTP OPTIONS requests, listing patch document media type(s) supported by the server. 4.2.8 HTTP OPTIONS
This specification imposes the following new requirements on HTTP OPTIONS for LDPRs beyond those in [RFC7231]. Other sections of this specification, for example PATCH, Accept-Post, add other requirements on OPTIONS responses.
OPTIONS method. 4.2.8.2 LDP servers MUST indicate their support for HTTP Methods by responding to a HTTP OPTIONS request on the LDPR’s URL with the HTTP Method tokens in the HTTP response header Allow. 4.3 RDF Source
The following section contains normative clauses for Linked Data Platform RDF Source.
4.3.1 General 4.3.1.1 Each LDP RDF Source MUST also be a conforming LDP Resource as defined in section 4.2 Resource, along with the restrictions in this section. LDP clients MAY infer the following triple: one whose subject is the LDP-RS, whose predicate isrdf:type, and whose object is ldp:Resource, but there is no requirement to materialize this triple in the LDP-RS representation. 4.3.1.2 LDP-RSs representations SHOULD have at least one rdf:type set explicitly. This makes the representations much more useful to client applications that don’t support inferencing. 4.3.1.3 The representation of a LDP-RS MAY have an rdf:type of ldp:RDFSource for Linked Data Platform RDF Source. 4.3.1.4 LDP servers MUST provide an RDF representation for LDP-RSs. The HTTP Request-URI of the LDP-RS is typically the subject of most triples in the response. 4.3.1.5 LDP-RSs SHOULD reuse existing vocabularies instead of creating their own duplicate vocabulary terms. In addition to this general rule, some specific cases are covered by other conformance rules. 4.3.1.6 LDP-RSs predicates SHOULD use standard vocabularies such as Dublin Core [DC-TERMS], RDF [rdf11-concepts] and RDF Schema [rdf-schema], whenever possible. 4.3.1.7 In the absence of special knowledge of the application or domain, LDP clients MUST assume that any LDP-RS can have multiple rdf:type triples with different objects. 4.3.1.8 In the absence of special knowledge of the application or domain, LDP clients MUST assume that the rdf:type values of a given LDP-RS can change over time. 4.3.1.9 LDP clients SHOULD always assume that the set of predicates for a LDP-RS of a particular type at an arbitrary server is open, in the sense that different resources of the same type may not all have the same set of predicates in their triples, and the set of predicates that are used in the state of any one LDP-RS is not limited to any pre-defined set. 4.3.1.10 LDP servers MUST NOT require LDP clients to implement inferencing in order to recognize the subset of content defined by LDP. Other specifications built on top of LDP may require clients to implement inferencing [rdf11-concepts]. The practical implication is that all content defined by LDP must be explicitly represented, unless noted otherwise within this document. 4.3.1.11 A LDP client MUST preserve all triples retrieved from a LDP-RS using HTTP GET that it doesn’t change whether it understands the predicates or not, when its intent is to perform an update using HTTP PUT. The use of HTTP PATCH instead of HTTP PUT for update avoids this burden for clients [RFC5789]. 4.3.1.12 LDP clients MAY provide LDP-defined hints that allow servers to optimize the content of responses. section 7.2 Preferences on the Prefer Request Header defines hints that apply to LDP-RSs. 4.3.1.13 LDP clients MUST be capable of processing responses formed by a LDP server that ignores hints, including LDP-defined hints. 4.3.2 HTTP GET 4.3.2.1 LDP servers MUST respond with a Turtle representation of the requested LDP-RS when the request includes an Accept header specifying text/turtle, unless HTTP content negotiation requires a different outcome [turtle].
Non-normative note: In other words, Turtle must be returned by LDP servers in the usual case clients would expect (client requests it) as well as cases where the client requests Turtle or other media type(s), content negotiation results in a tie, and Turtle is one of the tying media types. For example, if the4.3.2.2 LDP servers SHOULD respond with aAcceptheader liststext/turtleas one of several media types with the highest relative quality factor (q=value), LDP servers must respond with Turtle. HTTP servers in general are not required to resolve ties in this way, or to support Turtle at all, but LDP servers are. On the other hand, if Turtle is one of several requested media types, but another media type the server supports has a higher relative quality factor, standard HTTP content negotiation rules apply and the server (LDP or not) would not respond with Turtle.
text/turtle representation of the requested LDP-RS whenever the Accept request header is absent [turtle]. 4.3.2.3 LDP servers MUST respond with a application/ld+json representation of the requested LDP-RS when the request includes an Accept header, unless content negotiation or Turtle support requires a different outcome [JSON-LD]. 4.4 Non-RDF Source
The following section contains normative clauses for Linked Data Platform Non-RDF Source.
4.4.1 General 4.4.1.1 Each LDP Non-RDF Source MUST also be a conforming LDP Resource in section 4.2 Resource. LDP Non-RDF Sources may not be able to fully express their state using RDF [rdf11-concepts]. 4.4.1.2 LDP servers exposing an LDP Non-RDF Source MAY advertise this by exposing a HTTPLink header with a target URI of http://www.w3.org/ns/ldp#NonRDFSource, and a link relation type of type (that is, rel="type") in responses to requests made to the LDP-NR's HTTP Request-URI [RFC5988]. 5. Linked Data Platform Containers 5.1 Introduction
This section is non-normative.
Many HTTP applications and sites have organizing concepts that partition the overall space of resources into smaller containers. Blog posts are grouped into blogs, wiki pages are grouped into wikis, and products are grouped into catalogs. Each resource created in the application or site is created within an instance of one of these container-like entities, and users can list the existing artifacts within one. Containers answer some basic questions, which are:
This document defines the representation and behavior of containers that address these issues. There are multiple types of containers defined to support a variety of use cases, all that support a base set of capabilities. The contents of a container is defined by a set of triples in its representation (and state) called the containment triples that follow a fixed pattern. Additional types of containers allow for the set of members of a container to be defined by a set of triples in its representation called the membership triples that follow a consistent pattern (see the linked-to definition for the possible patterns). The membership triples of a container all have the same predicate, called the membership predicate, and either the subject or the object is also a consistent value – the remaining position of the membership triples (the one that varies) define the members of the container. In the simplest cases, the consistent value will be the LDPC resource's URI, but it does not have to be. The membership predicate is also variable and will often be a predicate from the server application vocabulary or the ldp:member predicate.
In LDP 1.0, there exists a way for clients to request responses that contain only partial representations of the containers. Applications may define additional means by which the response representations contain a filtered set of data and including (or excluding) additional details, those means are application-specific and not defined in this document.
This document includes a set of guidelines for creating new resources and adding them to the list of resources linked to a container. It goes on to explain how to learn about a set of related resources, regardless of how they were created or added to the container's membership. It also defines behavior when resources created using a container are later deleted; deleting containers removes membership information and possibly performs some cleanup tasks on unreferenced member resources.
The following illustrates a very simple container with only three members and some information about the container (the fact that it is a container and a brief title):
Request tohttp://example.org/c1/:
Example 1
GET /c1/ HTTP/1.1 Host: example.org Accept: text/turtleResponse:
Example 2
HTTP/1.1 200 OK
Content-Type: text/turtle
Date: Thu, 12 Jun 2014 18:26:59 GMT
ETag: "8caab0784220148bfe98b738d5bb6d13"
Accept-Post: text/turtle, application/ld+json
Allow: POST,GET,OPTIONS,HEAD,PUT
Link: <http://www.w3.org/ns/ldp#BasicContainer>; rel="type",
<http://www.w3.org/ns/ldp#Resource>; rel="type"
Transfer-Encoding: chunked
@prefix dcterms: <http://purl.org/dc/terms/>.
@prefix ldp: <http://www.w3.org/ns/ldp#>.
<http://example.org/c1/>
a ldp:BasicContainer;
dcterms:title "A very simple container";
ldp:contains <r1>, <r2>, <r3>.
The preceding example is very straightforward: there are containment triples whose subject is the container, whose predicate is ldp:contains, and whose objects are the URIs of the contained resources, and there is no distinction between member resources and contained resources. A POST to this container will create a new resource and add it to the list of contained resources by adding a new containment triple to the container. This type of container is called a Linked Data Platform Basic Container.
Sometimes you have to build on existing models incrementally, so you have fewer degrees of freedom in the resource model. In these situations, it can be useful to help clients map LDP patterns onto existing vocabularies, or to include members not created via the container; LDP Direct Containers meet those kinds of needs. Direct Containers allow membership triples to use a subject other than the container itself as the consistent membership value, and/or to use a predicate from an application's domain model as the membership predicate.
Let's start with a pre-existing domain resource for a person's net worth, as illustrated immediately below, and then see how a Container resource can be applied in subsequent examples:
Request tohttp://example.org/netWorth/nw1/:
Example 3
GET /netWorth/nw1/ HTTP/1.1 Host: example.org Accept: text/turtleResponse:
Example 4
HTTP/1.1 200 OK
Content-Type: text/turtle
Date: Thu, 12 Jun 2014 18:26:59 GMT
ETag: "0f6b5bd8dc1f754a1238a53b1da34f6b"
Link: <http://www.w3.org/ns/ldp#RDFSource>; rel="type",
<http://www.w3.org/ns/ldp#Resource>; rel="type"
Allow: GET,OPTIONS,HEAD,PUT,DELETE
Transfer-Encoding: chunked
@prefix ldp: <http://www.w3.org/ns/ldp#>.
@prefix o: <http://example.org/ontology#>.
<http://example.org/netWorth/nw1/>
a o:NetWorth;
o:netWorthOf <http://example.org/users/JohnZSmith>;
o:asset
<assets/a1>,
<assets/a2>;
o:liability
<liabilities/l1>,
<liabilities/l2>,
<liabilities/l3>.
In the preceding example, there is a rdf:type of o:NetWorth indicating the resource represents an instance of a person's net worth and a o:netWorthOf predicate indicating the associated person. There are two sets of same-subject, same-predicate triples; one for assets and one for liabilities. Existing domain-specific applications exist that depend on those types and predicates, so changing them incompatibly would be frowned upon.
It would be helpful to be able to use LDP patterns to manage the assets and liabilities-related triples. Doing so using a Basic Container would require duplicating much of the information with different types and predicates, which would be onerous for large resources. Direct Containers provide a middle ground, by giving LDP clients a way to map existing domain-specific resources to LDP's types and interaction models. In this specific example, it would be helpful to be able to manage the assets and liabilities triples consistently, for example by using LDP containers. One way to do this is to create two containers, one to manage assets and another liabilities, as separate HTTP resources. Existing clients have no need to interact with those containers, whereas LDP-enabled clients now have container URLs that they can interact with. The existing resource remains unchanged so that existing clients continue to function normally. This is illustrated in the set of related examples, one example per HTTP resource, starting with the LDP-RS example from before:
Request tohttp://example.org/netWorth/nw1/:
Example 5
GET /netWorth/nw1/ HTTP/1.1 Host: example.org Accept: text/turtleResponse:
Example 6
HTTP/1.1 200 OK
Content-Type: text/turtle
Date: Thu, 12 Jun 2014 18:26:59 GMT
ETag: "0f6b5bd8dc1f754a1238a53b1da34f6b"
Link: <http://www.w3.org/ns/ldp#RDFSource>; rel="type",
<http://www.w3.org/ns/ldp#Resource>; rel="type"
Allow: GET,OPTIONS,HEAD,PUT,DELETE
Transfer-Encoding: chunked
@prefix ldp: <http://www.w3.org/ns/ldp#>.
@prefix o: <http://example.org/ontology#>.
<http://example.org/netWorth/nw1/>
a o:NetWorth;
o:netWorthOf <http://example.org/users/JohnZSmith>;
o:asset
<assets/a1>,
<assets/a2>;
o:liability
<liabilities/l1>,
<liabilities/l2>,
<liabilities/l3>.
The structure of the net worth resource is completely unchanged, so any existing domain-specific applications continue to work without impact. LDP clients, on the other hand, have no way to understand that the asset and liability triples correspond in any way to LDP containers. For that, they need the next two resources.
The first container is a LDP Direct Container to manage assets. Direct Containers add the concept of membership and flexibility on how to specify the membership triples.
Request tohttp://example.org/netWorth/nw1/assets/:
Example 7
GET /netWorth/nw1/assets/ HTTP/1.1 Host: example.org Accept: text/turtleResponse:
Example 8
HTTP/1.1 200 OK
Content-Type: text/turtle
Date: Thu, 12 Jun 2014 18:26:59 GMT
ETag: "6df36eef2631a1795bfe9ab76760ea75"
Accept-Post: text/turtle, application/ld+json
Allow: POST,GET,OPTIONS,HEAD
Link: <http://www.w3.org/ns/ldp#DirectContainer>; rel="type",
<http://www.w3.org/ns/ldp#Resource>; rel="type"
Transfer-Encoding: chunked
@prefix ldp: <http://www.w3.org/ns/ldp#>.
@prefix dcterms: <http://purl.org/dc/terms/>.
@prefix o: <http://example.org/ontology#>.
<http://example.org/netWorth/nw1/assets/>
a ldp:DirectContainer;
dcterms:title "The assets of JohnZSmith";
ldp:membershipResource <http://example.org/netWorth/nw1/>;
ldp:hasMemberRelation o:asset;
ldp:contains <a1>, <a2>.
In the preceding asset container, the consistent membership value (membership-constant-URI, still in the subject position) is not the container itself – it is the (separate) net worth resource. The membership predicate is o:asset, from the domain model. A POST of an asset representation to the asset container will create a new asset and add it to net-worth's list of assets by adding a new membership triple to the resource and a containment triple to the container.
The second container is a LDP Direct Container to manage liabilities.
Request tohttp://example.org/netWorth/nw1/liabilities/:
Example 9
GET /netWorth/nw1/liabilities/ HTTP/1.1 Host: example.org Accept: text/turtleResponse:
Example 10
HTTP/1.1 200 OK
Content-Type: text/turtle
Date: Thu, 12 Jun 2014 18:26:59 GMT
ETag: "9f50da01f792281ddcfebe9788372d07"
Link: <http://www.w3.org/ns/ldp#DirectContainer>; rel="type",
<http://www.w3.org/ns/ldp#Resource>; rel="type"
Accept-Post: text/turtle, application/ld+json
Allow: POST,GET,OPTIONS,HEAD
Transfer-Encoding: chunked
@prefix ldp: <http://www.w3.org/ns/ldp#>.
@prefix dcterms: <http://purl.org/dc/terms/>.
@prefix o: <http://example.org/ontology#>.
<http://example.org/netWorth/nw1/liabilities/>
a ldp:DirectContainer;
dcterms:title "The liabilities of JohnZSmith";
ldp:membershipResource <http://example.org/netWorth/nw1/>;
ldp:hasMemberRelation o:liability;
ldp:contains <l1>, <l2>, <l3>.
The preceding liability container is completely analogous to the asset container above, simply managing liabilities instead of assets and using the o:liability predicate.
To add a another liability, a client would POST something like this to the liability container:
Request tohttp://example.org/netWorth/nw1/liabilities/:
Example 11
POST /netWorth/nw1/liabilities/ HTTP/1.1 Host: example.org Accept: text/turtle Content-Type: text/turtle Content-Length: 63 @prefix o: <http://example.org/ontology#>. <> a o:Liability. # plus any other properties that the domain says liabilities haveResponse:
Example 12
HTTP/1.1 201 Created
Location: http://example.org/netWorth/nw1/liabilities/l4
Date: Thu, 12 Jun 2014 19:56:13 GMT
Link: <http://www.w3.org/ns/ldp#DirectContainer>; rel="type",
<http://www.w3.org/ns/ldp#Resource>; rel="type"
Assuming the server successfully processes this request and assigns the URI <http://example.org/netWorth/nw1/liabilities/l4> to the newly created liability resource, at least two new triples would be added.
<http://example.org/netWorth/nw1/> o:liability <liabilities/l4><http://example.org/netWorth/nw1/liabilities/> ldp:contains <l4>.You might wonder why we chose to create two new containers instead of making http://example.org/netWorth/nw1/ itself a container. A single net worth container would be a fine design if http://example.org/netWorth/nw1/ had only assets or only liabilities (basically: only a single predicate to manage), but since it has separate predicates for assets and liabilities an ambiguity arises: it is unspecified whether a client's creation request (POST) should add a new o:asset or o:liability triple. Having separate http://example.org/netWorth/nw1/assets/ and http://example.org/netWorth/nw1/liabilities/ containers allows both assets and liabilities to be created and linked to the net-worth resource using the appropriate predicate. Similar ambiguities arise if the client wishes to list the members and/or contained resources.
Continuing in the multiple containers direction, we will now extend our net worth example to add a container for advisors (people) that have managed the assets and liabilities. We have decided to identify these advisors with URLs that contain a fragment (hash) to represent these real-world resources, not the documents that describe them.
Request tohttp://example.org/netWorth/nw1/:
Example 13
GET /netWorth/nw1/ HTTP/1.1 Host: example.org Accept: text/turtleResponse:
Example 14
HTTP/1.1 200 OK
Content-Type: text/turtle
Date: Thu, 12 Jun 2014 18:26:59 GMT
ETag: "e8d129f45ca31848fb56213844a32b49"
Link: <http://www.w3.org/ns/ldp#DirectContainer>; rel="type",
<http://www.w3.org/ns/ldp#Resource>; rel="type"
Allow: GET,OPTIONS,HEAD,PUT,DELETE
Transfer-Encoding: chunked
@prefix ldp: <http://www.w3.org/ns/ldp#>.
@prefix dcterms: <http://purl.org/dc/terms/>.
@prefix foaf: <http://xmlns.com/foaf/0.1/>.
@prefix o: <http://example.org/ontology#>.
<http://example.org/netWorth/nw1/>
a o:NetWorth;
o:netWorthOf <http://example.org/users/JohnZSmith>;
o:advisor
<advisors/bob#me>, # URI of a person
<advisors/marsha#me>.
<advisors/>
a ldp:IndirectContainer;
dcterms:title "The asset advisors of JohnZSmith";
ldp:membershipResource <>;
ldp:hasMemberRelation o:advisor;
ldp:insertedContentRelation foaf:primaryTopic;
ldp:contains
<advisors/bob>, # URI of a document a.k.a. an information resource
<advisors/marsha>. # describing a person
To handle this type of indirection, the triple with predicate of ldp:insertedContentRelation and object of foaf:primaryTopic informs clients that when POSTing to this container, they need to include a triple of the form (<>, foaf:primaryTopic, topic-URI) to inform the server which URI to use (topic-URI) in the new membership triple.
This type of container is referred to as a LDP Indirect Container. It is similar to an LDP Direct Container but it provides an indirection to add (via a create request) as a member any resource, including a URI representing a real-world object. Create requests to LDP Direct Containers can only add information resources [WEBARCH] - the documents they create - as members.
To add a another advisor, a client would POST something like this to the advisors container:
Request tohttp://example.org/netWorth/nw1/advisors/:
Example 15
POST /netWorth/nw1/advisors/ HTTP/1.1 Host: example.org Accept: text/turtle Content-Type: text/turtle Slug: george Content-Length: 72 @prefix foaf: <http://xmlns.com/foaf/0.1/>. @prefix o: <http://example.org/ontology#>. <> a o:Advisor; foaf:primaryTopic <#me>. # plus any other properties that the domain says advisors haveResponse:
Example 16
HTTP/1.1 201 Created
Location: http://example.org/netWorth/nw1/advisors/george
Date: Thu, 12 Jun 2014 19:56:13 GMT
Link: <http://www.w3.org/ns/ldp#RDFSource>; rel="type",
<http://www.w3.org/ns/ldp#Resource>; rel="type"
Assuming the server successfully processes this request and assigns the URI <http://example.org/netWorth/nw1/advisors/george> to the newly created advisor resource, at least two new triples would be added.
<http://example.org/netWorth/nw1/> o:advisor <advisors/george#me><http://example.org/netWorth/nw1/advisors/> ldp:contains <george>In summary, Fig. 3 Class relationship of types of Linked Data Platform Containers illustrates the LDP-defined container types: Basic, Direct, and Indirect, along with their class relationship to types of LDPRs.
Fig. 3 Class relationship of types of Linked Data Platform ContainersThe following table illustrates some differences between membership and containment triples. For details on the normative behavior, see appropriate sections below.
Completed Request Effects Membership Containment LDPR created in LDP-BC New triple: (LDPC, ldp:contains, LDPR) Same LDPR created in LDP-DC New triple links LDP-RS to created LDPR. LDP-RS URI may be same as LDP-DC New triple: (LDPC, ldp:contains, LDPR) LDPR created in LDP-IC New triple links LDP-RS to content indicated URI New triple: (LDPC, ldp:contains, LDPR) LDPR is deleted Membership triple may be removed (LDPC, ldp:contains, LDPR) triple is removed LDPC is deleted Triples and member resources may be removed Triples of form (LDPC, ldp:contains, LDPR) and contained LDPRs may be removed 5.1.1 Retrieving Only Minimal-Container TriplesThe representation of a container that has many members will be large. There are several important cases where clients need to access only the subset of the container's properties that are unrelated to member resources and unrelated to contained documents, for example to determine the membership triple pattern and membership predicate of an LDP-DC. LDP calls these minimal-container triples, because they are what remains when the container has zero members and zero contained resources. Since retrieving the whole container representation to get this information may be onerous for clients and cause unnecessary overhead on servers, we define a way to retrieve only these property values (and more generally, a way to retrieve only the subset of properties used to address other major clusters of use cases). LDP adds parameters to the HTTP Prefer header's return=representation preference for this (see section 7.2 Preferences on the Prefer Request Header for details).
The example listed here only shows a simple case where few minimal-container triples are retrieved. In real world situations more complex cases are likely, such as those that add other predicates to containers, for example providing validation information and associating SPARQL endpoints. [sparql11-query]
Here is an example requesting the minimal-container triples of a container identified by the URL http://example.org/container1/.
Request to http://example.org/container1/:
Example 17
GET /container1/ HTTP/1.1 Host: example.org Accept: text/turtle Prefer: return=representation; include="http://www.w3.org/ns/ldp#PreferMinimalContainer"
Response:
Example 18
HTTP/1.1 200 OK
Content-Type: text/turtle
ETag: "_87e52ce291112"
Link: <http://www.w3.org/ns/ldp#DirectContainer>; rel="type",
<http://www.w3.org/ns/ldp#Resource>; rel="type"
Accept-Post: text/turtle, application/ld+json
Allow: POST,GET,OPTIONS,HEAD
Preference-Applied: return=representation
Transfer-Encoding: chunked
@prefix dcterms: <http://purl.org/dc/terms/>.
@prefix ldp: <http://www.w3.org/ns/ldp#>.
<http://example.org/container1/>
a ldp:DirectContainer;
dcterms:title "A Linked Data Platform Container of Acme Resources";
ldp:membershipResource <http://example.org/container1/>;
ldp:hasMemberRelation ldp:member;
ldp:insertedContentRelation ldp:MemberSubject;
dcterms:publisher <http://acme.com/>.
LDP recommends using PATCH to update these properties, if necessary. It provides no facility for updating them via PUT without replacing the entire container's state.
5.2 ContainerThe following section contains normative clauses for Linked Data Platform Container.
5.2.1 GeneralThe Linked Data Platform does not define how clients discover LDPCs.
5.2.1.1 Each Linked Data Platform Container MUST also be a conforming Linked Data Platform RDF Source. LDP clients MAY infer the following triple: one whose subject is the LDPC, whose predicate isrdf:type, and whose object is ldp:RDFSource, but there is no requirement to materialize this triple in the LDPC representation. 5.2.1.2 The representation of a LDPC MAY have an rdf:type of ldp:Container for Linked Data Platform Container. Non-normative note: LDPCs might have additional types, like any LDP-RS. 5.2.1.3 LDPC representations SHOULD NOT use RDF container types rdf:Bag, rdf:Seq or rdf:List. 5.2.1.4 LDP servers exposing LDPCs MUST advertise their LDP support by exposing a HTTP Link header with a target URI matching the type of container (see below) the server supports, and a link relation type of type (that is, rel="type") in all responses to requests made to the LDPC's HTTP Request-URI. LDP servers MAY provide additional HTTP Link: rel="type" headers. The notes on the corresponding LDPR constraint apply equally to LDPCs.
5.2.1.5 LDP servers SHOULD respect all of a client's LDP-defined hints, for example which subsets of LDP-defined state the client is interested in processing, to influence the set of triples returned in representations of a LDPC, particularly for large LDPCs. See also [LDP-PAGING]. 5.2.2 HTTP GETValid container type URIs for
rel="type"defined by this document are:
http://www.w3.org/ns/ldp#BasicContainer- for LDP Basic Containershttp://www.w3.org/ns/ldp#DirectContainer- for LDP Direct Containershttp://www.w3.org/ns/ldp#IndirectContainer- for LDP Indirect Containers
Per section 4.2.2 HTTP GET the HTTP GET method is required and additional requirements can be found in section 5.2.1 General.
5.2.3 HTTP POSTPer [RFC7231], this HTTP method is optional and this specification does not require LDP servers to support it. When a LDP server supports this method, this specification imposes the following new requirements for LDPCs.
Any server-imposed constraints on creation or update must be advertised to clients.
5.2.3.1 LDP clients SHOULD create member resources by submitting a representation as the entity body of the HTTPPOST to a known LDPC. If the resource was created successfully, LDP servers MUST respond with status code 201 (Created) and the Location header set to the new resource’s URL. Clients shall not expect any representation in the response entity body on a 201 (Created) response. 5.2.3.2 When a successful HTTP POST request to a LDPC results in the creation of a LDPR, a containment triple MUST be added to the state of the LDPC whose subject is the LDPC URI, whose predicate is ldp:contains and whose object is the URI for the newly created document (LDPR). Other triples may be added as well. The newly created LDPR appears as a contained resource of the LDPC until the newly created document is deleted or removed by other methods. 5.2.3.3 LDP servers MAY accept an HTTP POST of non-RDF representations (LDP-NRs) for creation of any kind of resource, for example binary resources. See the Accept-Post section for details on how clients can discover whether a LDPC supports this behavior. 5.2.3.4 LDP servers that successfully create a resource from a RDF representation in the request entity body MUST honor the client's requested interaction model(s). If any requested interaction model cannot be honored, the server MUST fail the request.
5.2.3.5 LDP servers that allow creation of LDP-RSs via POST MUST allow clients to create new members by enclosing a request entity body with a
- If the request header specifies a LDPR interaction model, then the server MUST handle subsequent requests to the newly created resource's URI as if it is a LDPR. When the server treats the resource as a LDPR, then clients can only depend upon behaviors defined by LDPRs, even if the content contains an
rdf:typetriple indicating a type of LDPC. That is, if the server's statement conflicts with the content's, the server's statement wins.- If the request header specifies a LDPC interaction model, then the server MUST handle subsequent requests to the newly created resource's URI as if it is a LDPC.
- This specification does not constrain the server's behavior in other cases.
Clients use the same syntax, that is
HTTP Linkheaders, to specify the desired interaction model when creating a resource as servers use to advertise it on responses.Note: A consequence of this is that LDPCs can be used to create LDPCs, if the server supports doing so.
Non-normative note: LDP assumes that the interaction model of a resource is fixed when the resource is created, and this is reflected in the language of the bullets. If an implementation were to extend LDP by allowing the interaction model to vary after creation, that is viewed as a compatible extension to LDP and the statements above would constrain the default interaction model rather than saying that no other behavior is possible.
Content-Type request header whose value is text/turtle [turtle]. 5.2.3.6 LDP servers SHOULD use the Content-Type request header to determine the request representation's format when the request has an entity body. 5.2.3.7 LDP servers creating a LDP-RS via POST MUST interpret the null relative URI for the subject of triples in the LDP-RS representation in the request entity body as identifying the entity in the request body. Commonly, that entity is the model for the "to be created" LDPR, so triples whose subject is the null relative URI result in triples in the created resource whose subject is the created resource. 5.2.3.8 LDP servers SHOULD assign the URI for the resource to be created using server application specific rules in the absence of a client hint. 5.2.3.9 LDP servers SHOULD allow clients to create new resources without requiring detailed knowledge of application-specific constraints. This is a consequence of the requirement to enable simple creation and modification of LDPRs. LDP servers expose these application-specific constraints as described in section 4.2.1 General. 5.2.3.10 LDP servers MAY allow clients to suggest the URI for a resource created through POST, using the HTTP Slug header as defined in [RFC5023]. LDP adds no new requirements to this usage, so its presence functions as a client hint to the server providing a desired string to be incorporated into the server's final choice of resource URI. 5.2.3.11 LDP servers that allow member creation via POST SHOULD NOT re-use URIs. 5.2.3.12 Upon successful creation of an LDP-NR (HTTP status code of 201-Created and URI indicated by Location response header), LDP servers MAY create an associated LDP-RS to contain data about the newly created LDP-NR. If a LDP server creates this associated LDP-RS, it MUST indicate its location in the response by adding a HTTP Link header with a context URI identifying the newly created LDP-NR (instead of the effective request URI), a link relation value of describedby, and a target URI identifying the associated LDP-RS resource [RFC5988]. 5.2.3.13 LDP servers that support POST MUST include an Accept-Post response header on HTTP OPTIONS responses, listing POST request media type(s) supported by the server. LDP only specifies the use of POST for the purpose of creating new resources, but a server can accept POST requests with other semantics. While "POST to create" is a common interaction pattern, LDP clients are not guaranteed, even when making requests to a LDP server, that every successful POST request will result in the creation of a new resource; they must rely on out of band information for knowledge of which POST requests, if any, will have the "create new resource" semantics. This requirement on LDP servers is intentionally stronger than the one levied in the header registration; it is unrealistic to expect all existing resources that support POST to suddenly return a new header or for all new specifications constraining POST to be aware of its existence and require it, but it is a reasonable requirement for new specifications such as LDP. 5.2.3.14 LDP servers that allow creation of LDP-RSs via POST MUST allow clients to create new members by enclosing a request entity body with a Content-Type request header whose value is application/ld+json [JSON-LD]. 5.2.4 HTTP PUT
Per [RFC7231], this HTTP method is optional and this specification does not require LDP servers to support it. When a LDP server supports this method, this specification imposes the following new requirements for LDPCs.
Any server-imposed constraints on creation or update must be advertised to clients.
5.2.4.1 LDP servers SHOULD NOT allow HTTPPUT to update a LDPC’s containment triples; if the server receives such a request, it SHOULD respond with a 409 (Conflict) status code. 5.2.4.2 LDP servers that allow LDPR creation via PUT SHOULD NOT re-use URIs. 5.2.5 HTTP DELETE
Per [RFC7231], this HTTP method is optional and this specification does not require LDP servers to support it. When a LDP server supports this method, this specification imposes the following new requirements for LDPCs.
5.2.5.1 When a contained LDPR is deleted, the LDPC server MUST also remove the corresponding containment triple, which has the effect of removing the deleted LDPR from the containing LDPC.Non-normative note: The LDP server might perform additional actions, as described in the normative references like [RFC7231]. For example, the server could remove membership triples referring to the deleted LDPR, perform additional cleanup tasks for resources it knows are no longer referenced or have not been accessed for some period of time, and so on.5.2.5.2 When a contained LDPR is deleted, and the LDPC server created an associated LDP-RS (see the LDPC POST section), the LDPC server MUST also delete the associated LDP-RS it created. 5.2.6 HTTP HEAD
Note that certain LDP mechanisms rely on HTTP headers, and HTTP recommends that HEAD responses include the same headers as GET responses. LDP servers must also include HTTP headers on responses to OPTIONS, see section 4.2.8 HTTP OPTIONS. Thus, implementers supporting HEAD should also carefully read the section 5.2.2 HTTP GET and section 5.2.8 HTTP OPTIONS.
Per [RFC5789], this HTTP method is optional and this specification does not require LDP servers to support it. When a LDP server supports this method, this specification imposes the following new requirements for LDPCs.
Any server-imposed constraints on LDPR creation or update must be advertised to clients.
5.2.7.1 LDP servers are RECOMMENDED to support HTTPPATCH as the preferred method for updating a LDPC's minimal-container triples. 5.2.8 HTTP OPTIONS
This specification imposes the following new requirements on HTTP OPTIONS for LDPCs. Note that support for this method is required for LDPCs, since it is required for LDPRs and LDPCs adhere to LDP-RS requirements.
request-URI is a LDP-NR with an associated LDP-RS, a LDPC server MUST provide the same HTTP Link response header as is required in the create response. 5.3 Basic
The following section contains normative clauses for Linked Data Platform Basic Container.
5.3.1 General 5.3.1.1 Each LDP Basic Container MUST also be a conforming LDP Container in section 5.2 Container along with the following restrictions in this section. LDP clients MAY infer the following triple: whose subject is the LDP Basic Container, whose predicate isrdf:type, and whose object is ldp:Container, but there is no requirement to materialize this triple in the LDP-BC representation. 5.4 Direct
The following section contains normative clauses for Linked Data Platform Direct Container.
5.4.1 General 5.4.1.1 Each LDP Direct Container MUST also be a conforming LDP Container in section 5.2 Container along the following restrictions. LDP clients MAY infer the following triple: whose subject is the LDP Direct Container, whose predicate isrdf:type, and whose object is ldp:Container, but there is no requirement to materialize this triple in the LDP-DC representation. 5.4.1.2 LDP Direct Containers SHOULD use the ldp:member predicate as a LDPC's membership predicate if there is no obvious predicate from an application vocabulary to use. The state of a LDPC includes information about which resources are its members, in the form of membership triples that follow a consistent pattern. The LDPC's state contains enough information for clients to discern the membership predicate, the other consistent membership value used in the container's membership triples (membership-constant-URI), and the position (subject or object) where those URIs occurs in the membership triples. Member resources can be any kind of resource identified by a URI, LDPR or otherwise. 5.4.1.3 Each LDP Direct Container representation MUST contain exactly one triple whose subject is the LDPC URI, whose predicate is the ldp:membershipResource, and whose object is the LDPC's membership-constant-URI. Commonly the LDPC's URI is the membership-constant-URI, but LDP does not require this. 5.4.1.4 Each LDP Direct Container representation MUST contain exactly one triple whose subject is the LDPC URI, and whose predicate is either ldp:hasMemberRelation or ldp:isMemberOfRelation. The object of the triple is constrained by other sections, such as ldp:hasMemberRelation or ldp:isMemberOfRelation, based on the membership triple pattern used by the container. 5.4.1.4.1 LDP Direct Containers whose membership triple pattern is ( membership-constant-URI , membership-predicate , member-derived-URI ) MUST contain exactly one triple whose subject is the LDPC URI, whose predicate is ldp:hasMemberRelation, and whose object is the URI of membership-predicate. 5.4.1.4.2 LDP Direct Containers whose membership triple pattern is ( member-derived-URI , membership-predicate , membership-constant-URI ) MUST contain exactly one triple whose subject is the LDPC URI, whose predicate is ldp:isMemberOfRelation, and whose object is the URI of membership-predicate. 5.4.1.5 LDP Direct Containers MUST behave as if they have a ( LDPC URI, ldp:insertedContentRelation , ldp:MemberSubject ) triple, but LDP imposes no requirement to materialize such a triple in the LDP-DC representation. The value ldp:MemberSubject means that the member-derived-URI is the URI assigned by the server to a document it creates; for example, if the client POSTs content to a container that causes the container to create a new LDPR, ldp:MemberSubject says that the member-derived-URI is the URI assigned to the newly created LDPR. 5.4.2 HTTP POST 5.4.2.1 When a successful HTTP POST request to a LDPC results in the creation of a LDPR, the LDPC MUST update its membership triples to reflect that addition, and the resulting membership triple MUST be consistent with any LDP-defined predicates it exposes. A LDP Direct Container's membership triples MAY also be modified via through other means. 5.4.3 HTTP DELETE 5.4.3.1 When a LDPR identified by the object of a membership triple which was originally created by the LDP-DC is deleted, the LDPC server MUST also remove the corresponding membership triple. 5.5 Indirect
The following section contains normative clauses for Linked Data Platform Indirect Container.
5.5.1 General 5.5.1.1 Each LDP Indirect Container MUST also be a conforming LDP Direct Container as described in section 5.4 Direct, along with the following restrictions. LDP clients MAY infer the following triple: one whose subject is LDP Indirect Container, whose predicate isrdf:type, and whose object is ldp:Container, but there is no requirement to materialize this triple in the LDP-IC representation. 5.5.1.2 LDP Indirect Containers MUST contain exactly one triple whose subject is the LDPC URI, whose predicate is ldp:insertedContentRelation, and whose object ICR describes how the member-derived-URI in the container's membership triples is chosen. The member-derived-URI is taken from some triple ( S, P, O ) in the document supplied by the client as input to the create request; if ICR's value is P, then the member-derived-URI is O. LDP does not define the behavior when more than one triple containing the predicate P is present in the client's input. For example, if the client POSTs RDF content to a container that causes the container to create a new LDP-RS, and that content contains the triple ( <> , foaf:primaryTopic , bob#me ) foaf:primaryTopic says that the member-derived-URI is bob#me. One consequence of this definition is that indirect container member creation is only well-defined by LDP when the document supplied by the client as input to the create request has an RDF media type. 5.5.2 HTTP POST 5.5.2.1 LDPCs whose ldp:insertedContentRelation triple has an object other than ldp:MemberSubject and that create new resources MUST add a triple to the container whose subject is the container's URI, whose predicate is ldp:contains, and whose object is the newly created resource's URI (which will be different from the member-derived URI in this case). This ldp:contains triple can be the only link from the container to the newly created resource in certain cases. 6. Notable information from normative references
This section is non-normative.
While readers, and especially implementers, of LDP are assumed to understand the information in its normative references, the working group has found that certain points are particularly important to understand. For those thoroughly familiar with the referenced specifications, these points might seem obvious, yet experience has shown that few non-experts find all of them obvious. This section enumerates these topics; it is simply re-stating (non-normatively) information locatable via the normative references.
6.1 Architecture of the World Wide WebThis section is non-normative.
Reference: [WEBARCH] 6.1.1 LDPC membership is not exclusive; this means that the same resource (LDPR or not) can be a member of more than one LDPC. 6.1.2 LDP servers should not re-use URIs, regardless of the mechanism by which members are created (POST, PUT, etc.). Certain specific cases exist where a LDPC server might delete a resource and then later re-use the URI when it identifies the same resource, but only when consistent with Web architecture. While it is difficult to provide absolute implementation guarantees of non-reuse in all failure scenarios, re-using URIs creates ambiguities for clients that are best avoided. 6.2 HTTP 1.1
This section is non-normative.
Reference: [RFC7230], [RFC7231], [RFC7232] 6.2.1 LDP servers can support representations beyond those necessary to conform to this specification. These could be other RDF formats, like N3 or NTriples, but non-RDF formats like HTML [HTML401] and JSON [RFC4627] would likely be common. HTTP content negotiation ([RFC7231] Section 3.4 - Content Negotiation) is used to select the format. 6.2.2 LDPRs can be created, updated and deleted using methods not defined in this document, for example through application-specific means, SPARQL UPDATE, etc. [SPARQL-UPDATE], as long as those methods do not conflict with this specification's normative requirements. 6.2.3 LDP servers remove the resource identified by theRequest-URI in response to a successful HTTP DELETE request. After such a request, a subsequent HTTP GET on the same Request-URI usually results in a 404 (Not found) or 410 (Gone) status code, although HTTP allows others. 6.2.4 LDP servers can alter the state of other resources as a result of any HTTP request, especially when non-safe methods are used ([RFC7231] section 4.2.1). For example, it is acceptable for the server to remove triples from other resources whose subject or object is the deleted resource as the result of a successful HTTP DELETE request. It is also acceptable and common for LDP servers to not do this – the server's behavior can vary, so LDP clients cannot depend on it. 6.2.5 LDP servers can implement HTTP PATCH to allow modifications, especially partial replacement, of their resources. No minimal set of patch document formats is mandated by this document or by the definition of PATCH [RFC5789]. 6.2.6 When the Content-Type request header is absent from a request, LDP servers might infer the content type by inspecting the entity body contents ([RFC7231] section 3.1.1.5). 6.3 RDF
This section is non-normative.
Reference: [rdf11-concepts] 8. Link RelationsThe intent is that these link relations will be registered with IANA per [RFC5988] section 6.2.1.
8.1 describedbyThe contents of this section were originally taken from [POWDER] appendix D, and then modified to comply with the current registration template. The pre-LDP IANA link relation registry entry for describedby refers to a different section of [POWDER] that was substantively updated in an erratum, and that section was not actually the normative definition of the link relation. Since we expect no update to [POWDER] that incorporates the erratum or fixes the registry link, this superseding registration approach is being taken.
The following Link Relationship will be submitted to IANA for review, approval, and inclusion in the IANA Link Relations registry.
describedby
A describedby B asserts that resource B provides a description of resource A. There are no constraints on the format or representation of either A or B, neither are there any further constraints on either resource.
This section is non-normative.
As with any protocol that is implemented leveraging HTTP, implementations should take advantage of the many security-related facilities associated with it and are not required to carry out LDP operations that may be in contradistinction to a particular security policy in place. For example, when faced with an unauthenticated request to replace system critical RDF statements in a graph through the PUT method, applications may consider responding with the 401 status code (Unauthorized), indicating that the appropriate authorization is required. In cases where the provided authentication fails to meet the requirements of a particular access control policy, the 403 status code (Forbidden) can be sent back to the client to indicate this failure to meet the access control policy.
A. AcknowledgementsThis section is non-normative.
The following people have been instrumental in providing thoughts, feedback, reviews, content, criticism and input in the creation of this specification:
Arnaud Le Hors (chair), Alexandre Bertails, Andrei Sambra, Andy Seaborne, Antonis Loizou, Ashok Malhotra, Bart van Leeuwen, Cody Burleson, David Wood, Eric Prud'hommeaux, Erik Wilde, Henry Story, John Arwe, Kevin Page, Kingsley Idehen, Mark Baker, Martin P. Nally, Miel Vander Sande, Miguel Esteban Gutiérrez, Nandana Mihindukulasooriya, Olivier Berger, Pierre-Antoine Champin, Raúl García Castro, Reza B'Far, Richard Cyganiak, Rob Sanderson, Roger Menday, Ruben Verborgh, Sandro Hawke, Serena Villata, Sergio Fernandez, Steve Battle, Steve Speicher, Ted Thibodeau, Tim Berners-Lee, Yves Lafon
B. Change HistoryThis section is non-normative.
The change history is up to the editors to insert a brief summary of changes, ordered by most recent changes first and with heading from which public draft it has been changed from.
SummarySummary of notable changes from the Proposed Recommendation.
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