W3C Linked Data Platform Overview

© 2014 IBM Corporation
Linked Data Platform
7 October
W3C Linked Data Platform
Steve Speicher, @sspeiche
sspeiche@gmail.com

Agenda
2
Linked Data
■W3C Linked Data Platform
–LDP Resource
–LDP Container
–LDP Paging
Status
■Related Projects

Linked Data – Defined by Tim Berners-Lee
1. Use URIs as names for things
2. Use HTTP URIs so that people can look up those names.
3. When someone looks up a URI, provide useful information, using the standards (RDF*,
SPARQL)
4. Include links to other URIs. so that they can discover more things.
He concludes this with: “Simple.”
Reference: “Linked Data”, Tim Berners-Lee, 2006-07-27

Linked Data and the Web
 Linked Data is a natural extension of the web of documents:
4 October 7, 2014
Web of Documents Linked Data
Standard Global
Identifier+Locator
Pages are identified by a URL
which can also be used to
locate the page
Pieces of data are identified by a
URL which can also be used to
locate the data
Standard Access
Protocol
Pages are accessed via HTTP Data is accessed via HTTP
Standard
Representation
Pages are served in a standard
format: HTML
Data is served in a standard
representation: RDF
Standard way of
linking related items
Related pages are linked to one
another using their URLs
Related pieces of data are linked
to one another using their URLs

Not All Linked Data needs to be Linked Open Data (LOD)
Added in 2010 by Tim Berners-Lee: “in order to encourage people,
especially government data owners, along the road to good
linked data, I have developed this star rating system”
★ Available on the web (whatever format) but with an open licence, to be Open Data
★★ Available as machine-readable structured data (e.g. excel instead of image scan of
a table)
★★★ As (2) plus non-proprietary format (e.g. CSV instead of excel)
★★★★ All the above plus, Use open standards from W3C (RDF and SPARQL) to identify
things, so that people can point at your stuff
★★★★★ All the above, plus: Link your data to other people’s data to provide context
 This does NOT mean all Linked Data must be freely available.
 Just like not all web pages are publicly available not all Linked Data needs to be.

6
Software
Configuration
Management
Work-item & defect
tracking (aka Change
Management)
Build automation
& management
Test automation
& management
Requirements
management
Year 2010 – IBM Rational's Breakthrough
6
Integrate with data & open protocols instead of glue code
“If the entire Web can connect like this, why wouldn't the same idea work for ALM?”
Applying Linked Data to the ALM Integration Challenge:
 Artifacts such as defects, change requests, and tests become resources exposed as RDF
that can be linked to each other
 Tools simply access the resources via HTTP following the Linked Data principles

■ No formal definition
■ State of the art is primarily about publishing read-only data on the web, downloaded and
updated as large dumps or via a SPARQL entry point
■ Tim Berners-Lee's four principles are a terrific foundation but don’t go far enough.
■ Developers are left with many unanswered questions:
Challenges of using Linked Data
7
– How do I create a resource?
• It seems obvious that you use POST to create, but what do you POST to?
– Where can I get the list of resources that already exist?
– Which vocabulary do I use?
– Which media types do I use?
– When resources get big, how do I split the information into pages?
– How do I specify ordering?

Agenda
8
■Linked Data
W3C Linked Data Platform
–LDP Resource
–LDP Container
–LDP Paging
Status
■Related Projects

“A specification for HTTP-based (RESTful) application integration patterns using
read/write Linked Data.”
■A set of rules that clarify and extends Tim Berners-Lee's four basic rules focusing on the
following concepts:
Linked Data Platform (LDP)
9
– LDP Resources (LDPR)
– HTTP and RDF techniques to read and write linked data
– Resources can be created, modified, deleted and read using standard HTTP methods
(i.e., POST, PUT/PATCH, DELETE, GET).
– Cover “RDF sources” as well as “binary resources”
– LDP Containers (LDPC)
– An LDPR to which you POST to create new things, GET to find existing things
– Similar to what AtomPub does for XML
– Available in three flavors: BasicContainer, DirectContainer, and IndirectContainer
– Paging & Ordering
– A mechanism to get the content of an LDPR in chunks and specify the order in which
the content is sorted

Linked Data Platform Resource (LDPR)
Different types:
Some general rules:
1. LDPRs are HTTP resources that can be created, modified, deleted and read using standard
HTTP methods (i.e., POST, PUT/PATCH, DELETE, GET).
2. LDPRs use RDF to define their states.
3. You can request a Turtle representation of a LDPR and possibly other reps (e.g., XML/RDF)
4. LDP clients use Optimistic Collision Detection on update (etags).
This is little more than what HTTP already defines.

member1
http://example.org
LDP Resource – GET a simple example
GET /container1/member1 HTTP/1.1
Host: example.org
Accept: text/turtle
HTTP/1.1 200 OK
ETag: "_87e52ce291112"
Link: <http://www.w3.org/ns/ldp#Resource>; rel="type"
Allow: GET,PUT,PATCH,DELETE,OPTIONS,HEAD
@prefix dcterms: <http://purl.org/dc/terms/>.
@prefix ldp: <http://www.w3.org/ns/ldp#>.
<http://example.org/container1/member1>
a o:Cash;
dcterms:title “ACME Bank savings account”;
o:value 45.00.
Response Request
container1
member2
member3

Linked Data Platform Container (LDPC)
Different types:
Some general rules:
1. LDPCs are LDPRs
2. Clients can retrieve the list of resource members of an LDPC using GET
3. New resources are created by POSTing to an LDPC
4. Any resource can be POSTed to an LDPC – not just LDPRs (i.e., LDP-NR and LDPCs)
5. After POSTing a new resource to an LDPC, the new resource will appear as a member until
it is deleted.
6. Clients can retrieve information about an LDPC without retrieving a full representation of its
content, including its members.
7. On deleting an LDPC the server MAY delete member resources.

http://example.org
LDP BasicContainer – GET lists existing resources
GET /container1 HTTP/1.1
Host: example.org
Accept: text/turtle
Link: <http://www.w3.org/ns/ldp#BasicContainer>; rel="type",
<http://www.w3.org/ns/ldp#Resource>; rel="type"
Removed most HTTP headers to save some space
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>.
<http://example.org/container1>
a ldp:BasicContainer;
dcterms:title "A very simple container";
ldp:contains
<http://example.org/container1/member1>,
<http://example.org/container1/member3>.
Response Request
container1
member1
member2
member3

container1
member1
member2
member3
+member4
LDP BasicContainer – POST creates a new resource
POST /container1 HTTP/1.1
Host: example.org
Content-type: text/turtle
Content-length: 324
@prefix o: <http://example.org/ontology/>.
<>
a o:Stock;
dcterms:title “ACME Co.”;
o:value 100.00.
HTTP/1.1 201 CREATED
Content-Location: http://example.org/container1/member4
Response Request
http://example.org

container1
member1
member2
member3
member4
LDP BasicContainer – GET returns updated list
GET /container1 HTTP/1.1
Host: example.org
Accept: text/turtle
Removed HTTP headers to save some space
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>.
<http://example.org/container1>
a ldp:BasicContainer;
dcterms:title "A very simple container";
ldp:contains
<http://example.org/container1/member4>.
Response Request
http://example.org

Net worth example
Disclaimer: picture only in UML, does not follow UML constraints

LDP DirectContainer – Slightly more complex example
<http://example.org/netWorth/nw1>
a o:NetWorth;
o:asset
<http://example.org/netWorth/nw1/assetContainer/a1>,
<http://example.org/netWorth/nw1/assetContainer/a2>.
<http://example.org/netWorth/nw1/assetContainer>
a ldp:DirectContainer;
dcterms:title "The assets of JohnZSmith";
ldp:membershipResource <http://example.org/netWorth/nw1>;
ldp:hasMemberRelation o:asset.
• Members are associated with a resource other than the container
• Membership predicate is domain specific
• Relationship can take two different forms:
• <membershipResource> <ldp:hasMemberRelation> <member>
• <member> <ldp:isMemberOfRelation> <membershipResource>

LDP DirectContainer (continue)
a o:NetWorth;
o:asset
o:liability
<http://example.org/netWorth/nw1/liabilityContainer/l1>.
<http://example.org/netWorth/nw1/assetContainer>
dcterms:title "The assets of JohnZSmith";
ldp:hasMemberRelation o:asset.
<http://example.org/netWorth/nw1/liabilityContainer>
dcterms:title "The liabilities of JohnZSmith";
ldp:hasMemberRelation o:liability.
• Several containers can be defined around the same resource (e.g., assets, liabilities)

LDP IndirectContainer – More complex example
a o:NetWorth;
o:advisor
<advisorContainer/bob#me>,
<advisorContainer/marsha#me>.
<http://example.org/advisors/>
a ldp:IndirectContainer;
dcterms:title "The asset advisors of JohnZSmith";
ldp:hasMemberRelation o:advisor;
ldp:insertedContentRelation foaf:primaryTopic;
ldp:contains
<advisorContainer/bob>,
<advisorContainer/marsha>.
<http://example.org/advisorContainer/bob>
foaf:primaryTopic <#me>.
<#me> a foaf:Person;
foaf:name "Bob Marlow".
• Supports listing non-information resource as members

attachments
member1
member2
member3
+myimage
+myimage-info
LDP Non-RDF Sources a.k.a “Binary Resources”
POST /attachments/ HTTP/1.1
Host: example.org
Content-type: image/png
Content-length: 1048
Slug: myimage
[binary content not displayed]
HTTP/1.1 201 CREATED
Content-Location: http://example.org/attachments/myimage
Link: <http://example.org/mycontainer/myimage-info>;
rel=describedby
Response Request
 Created by POSTing to a Container
 As a result the server may create two resources:
– An LDP Non-RDF Source that is added as a member
– An LDP RDF Source that describes the LDP-NR
http://example.org

LDP Paging
GET /customer-relations HTTP/1.1
Host: example.org
Accept: text/turtle
Prefer: return=representation; max-triple-count="500"
HTTP/1.1 303 See Other
Location: <http://example.org/customer-relations?page1>
Response Request
 Client can request to only be sent a certain amount of data (# of triples, records, or kbytes)
 As a result the server may redirect to a first page

LDP Paging – Getting the first page
GET /customer-relations?page1 HTTP/1.1
Host: example.org
Accept: text/turtle
Request Response  Link Headers indicate: this is a page and provides link to the next page
HTTP/1.1 200 OK
Removed some HTTP headers to save some space
Link: <http://www.w3.org/ns/ldp#Resource>; rel="type",
<http://www.w3.org/ns/ldp#Page>; rel="type"
Link: <http://example.org/customer-relations?p=2>; rel='next'
Link: <http://example.org/customer-relations>; rel='canonical';
etag="customer-relations-v1”
Removed other prefix declarations
<>
a o:CustomerRelations;
dcterms:title "The customer information for Example Co.";
o:client <#JohnZSmith>, <#BettyASmith>, <#JoanRSmith>.
<#JohnZSmith>
a foaf:Person;
o:status o:ActiveCustomer;

Request  Link Header provides link to the resource being paged with etag to detect changes Response
LDP Paging – Detecting changes
GET /customer-relations?page1 HTTP/1.1
Host: example.org
Accept: text/turtle
HTTP/1.1 200 OK
<>
<#JohnZSmith>
a foaf:Person;
o:status o:ActiveCustomer;

LDP Paging – Optimizing workflow with HTTP 2NN
GET /customer-relations HTTP/1.1
Host: example.org
Accept: text/turtle
Prefer: contents-of-related
Request  When client supports 2NN, server can directly send first page back Response
HTTP/1.1 2NN Contents of Related
Location: <http://example.org/customer-relations?page1>
<>
<#JohnZSmith>
a foaf:Person;

LDP Paging – Ordering of LDP Containers
Link: ... <http://www.w3.org/ns/ldp#Page>; rel="type"
Link: <http://example.org/netWorth/nw1/assetContainer/sortedSequence/>;
Response
rel='http://www.w3.org/ns/ldp#pageSequence’
<> a ldp:DirectContainer;
ldp:hasMemberRelation o:asset;
ldp:insertedContentRelation ldp:MemberSubject;
ldp:contains <a1>, <a2>, <a3>.
a o:NetWorth; o:asset <a1>, <a3>, <a2>.
 Order used for paging is specified via a resource providing a list of sort criteria <a1> a o:Stock; o:marketValue 100.00 .
@base <http://example.org/netWorth/nw1/assetContainer/sortedSequence/> .
<> ldp:pageSortCriteria ( <#Sort-o.marketValue-Ascending> ).
<#Sort-o.marketValue-Ascending>
a ldp:pageSortCriterion;
ldp:pageSortOrder ldp:Ascending;
ldp:pageSortPredicate o:marketValue.

Agenda
26
■Linked Data
W3C Linked Data Platform
–LDP Resource
–LDP Container
–LDP Paging
Status
■Related Projects

Status
 Published Candidate Recommendation of LDP on 19 June 2014
27
–Proposed Recommendation expected by the end of September
– Test suite available for implementers
 About to publish Second Last Call of LDP Paging
–Provide for negotiation client-server
–Provide for more certainty
–Review period to end around the end of September 2014
 Updated Use Cases & Requirements WG Note on 13 March 2014
 Published Primer WG Note on 26 June 2014
 About to publish Best Practices & Guidelines WG Note
 About to publish Access Control Use cases & requirements WG Note
 About to publish First Public Working Draft of LD PATCH!
 Seeking feedback on direction!

Looking Forward
Several necessary and desirable features are not in scope for LDP 1.0:
■Security – Authentication, Access control
–WG is chartered to identify requirements and use cases
–Several technologies can already be used: OAuth, WebId, etc.
 Validation/Constraints
–RDFS and OWL are for inference not validation
– There is currently no standard technology to perform validation
• RDF Data Shapes Working Group has launched!
 Deployment challenges
–URL changes
–Server cloning
–Cross-server query
 LDP.Next Wish List: https://www.w3.org/2012/ldp/wiki/LDPNext

Agenda
29
■Linked Data
■W3C Linked Data Platform
–LDP Resource
–LDP Container
–LDP Paging
■Status
Related Projects

Several implementations are already available:
Implementation of LDP that can be extended and
deployed easily by organizations who want to publish
data or build custom applications
LDP Implementations
SDK and supporting tools to help the community to
adopt OSLC specifications and build compliant tools
Marmotta
For a more complete list see:
http://www.w3.org/wiki/LDP_Implementations

Automation
Monitoring
Open Services for Lifecycle Collaboration (OSLC)
Working to improve the way software lifecycle tools share data
Open Services for Lifecycle Collaboration
Lifecycle integration inspired by the web
 Community driven and governed
 400+ registered community members
 Workgroup members from 34+ organizations
 Wide range of interests, expertise, & participation
 Open specifications for numerous disciplines
 Defined by scenarios – solution oriented
 Implementations from IBM, BPs, and Others
 Based on Linked Data
Inspired by the web
Proven
Free to use and share
Open
Changing the industry
Innovative
open-services.net
For more info see: http://open-services.net

W3C Linked Data Platform Overview

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