Linked Data Platform zhengliang 2012.11.26

Outline Linked Data Linked Data Platform Linked Data principles LOD (Linking Open Data Project) Linked Data Platform Linked Data Platform Resource (LDPR) Linked Data Platform Container (LDPC)

Linked Data Linked Data refers to data published on the Web in such a way that it is machine-readable, its meaning is explicitly defined, it is linked to other external data sets, and can in turn be linked to from external data sets. Linked Data – The Story So Far Bizer C, Heath T, Berners-Lee T

Linked Data Linked Data principles Use URIs as names for things Use HTTP URIs so that people can look up those names When someone looks up a URI, provide useful information, using the standards(RDF, SPARQL) Include links to other URIs, so that they can discover more things Tim Berners-Lee 2007 http://www.w3.org/DesignIssues/LinkedData.html

Linked Data LOD (Linking Open Data Project) To extend the Web with a data commons by publishing various open data sets as RDF on the Web and by setting RDF links between data items from different data sources. include DBpedia ,DBLP Bibliography ,GeoNames and ….

Linked Data LOD Cloud Diagram

Linked Data (in Research and Practice) Research Challenges Publishing Linked Data on the Web User Interfaces and Interaction Paradigms Crawling, caching and querying Linked Data on the Web Linking algorithms and identity resolution Data integration and data fusion evaluating quality and trustworthiness of Linked Data …… Linked Data Applications Linked Data Browsers Linked Data Search Engines and Indexes Domain-specific Applications (LED…)

Linked Data Platform Linked Data Platform 1.0 (W3C Working Draft 25 October 2012) http://www.w3.org/TR/ldp/ describes the use of HTTP for accessing, updating, creating and deleting resources from servers that expose their resources as Linked Data.

Linked Data Platform Terminology Link Linked Data Linked Data Platform Resource (LDPR) Linked Data Platform Container (LDPC) Client Server

Linked Data Platform Resource (LDPR) are HTTP resources that conform to the simple patterns and conventions. HTTP requests to access, modify, create or delete LDPRs are accepted and processed by LDPR 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.

Linked Data Platform Resource (LDPR) address basic questions such as: What resource formats should be used?(RDF/RDFS/N3…) What literal value types should be used?([XMLSchema]…) Are there some typical vocabularies that should be reused?(Dublin Core…) How is optimistic collision detection handled for updates? What should client expectations be for changes to linked-to resources, such as type changes? What can servers do to ease the burden of constraints for resource creation?

Linked Data Platform Resource (LDPR) 4.2 HTTP GET 4.3 HTTP POST 4.4 HTTP PUT 4.4.1 If HTTP PUT is performed on an existing resource, LDPR servers must replace the entire persistent state of the identified resource with the entity representation in the body of the request. The only recognized exception are the properties dcterms:modified and dcterms:creator that are never under client control - LDPR servers must ignore any values of these properties that are provided by the client. Any LDPR 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.

Linked Data Platform Resource (LDPR) 4.4.2 LDPR 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. LDPR servers should require the HTTP If-Match header and HTTP ETags to detect collisions. 4.5 HTTP DELETE 4.5.1 LDPR servers must remove the resource identified by the Request-URI. After a successful HTTP DELETE, a subsequent HTTP GET on the same Request-URI must result in a 404 (Not found) or 410 (Gone) status code, until another resource is created or associated with the same Request-URI.

Linked Data Platform Resource (LDPR) 4.6 HTTP HEAD 4.7 HTTP PATCH 4.7.1 LDPR servers may implement HTTP PATCH to allow modifications, especially partial replacement, of their resources. 4.7.2 LDPR servers should allow clients to update resources without requiring detailed knowledge of server-specific constraints. It is common for LDPR servers to put restrictions on representations – for example, the range of rdf:type, datatypes of predicates and number of occurrences of predicates in triples – but server enforcement of detailed, domain-specific constraints will greatly restrict the types of clients who can update resources.

Linked Data Platform Container (LDPC) Many HTTP applications and sites have organizing concepts that partition the overall space of resources into smaller containers. answer some basic questions, which are: 1. To which URLs can I POST to create new resources? 2. Where can I GET a list of existing resources? 3. How is the order of the container entries expressed? 4. How do I get information about the members along with the container? 5. How do I GET the entries of a large container broken up into pages? 6. How can I ensure the resource data is easy to query?

Linked Data Platform Container (LDPC) the membership predicate is rdfs:member and the membership subject is the container itself

Linked Data Platform Container (LDPC) the membership subject is not the container itself – it is a separate net worth resource. Container predicate: ldp:membershipSubject, ldp:membershipPredicate.

Linked Data Platform Container (LDPC) Container Member Information Container a o:Networth Member a o:Stock … (from the domain model)

Linked Data Platform Container (LDPC) Paging the Request-URI of “<containerURL>?firstPage”, rdf:type is ldp:Page; ldp:pageOf is the URL of the LDPC. ldp:nextPage is being the URL for the subsequent page.

Linked Data Platform Container (LDPC) Paging rdf:nil: last page

Linked Data Platform Container (LDPC) 5.3 HTTP GET 5.4 HTTP POST 5.4.1 LDPC clients should create resources by submitting a representation as the entity body of the HTTP POST to a known LDPC. LDPC servers must respond with status code 201 (Created) and the Location header set to the new resource’s URL. 5.5 HTTP PUT 5.5.1 LDPC servers should not allow HTTP PUT to update a LDPC’s members and if the server receives such a request, it should respond with a 409 (Conflict) status code.

Linked Data Platform Container (LDPC) 5.6 HTTP DELETE 5.6.2 When a resource that is contained in a LDPC (for example referenced by a membership triple) is deleted, the server must also remove it from the LDPC that was used to create it and should remove it from any other containers that reference it that the server manages and persists. 5.7 HTTP HEAD There are no additional requirements on HTTP HEAD. 5.8 HTTP PATCH 5.8.1 LDPC servers are recommended to support HTTP PATCH as the preferred method for updating LDPC non-membership properties

Q&A Thanks! 1:container是否有类型？Must have . 而且可以是多types. 2：更新时冲突检测，只是简单的通过Etag查看，是否相同，避免重复更新。 并没有对资源语义中相同或相似的，即coreference进行检测。