The document describes how to model an address book application using the Linked Data Platform (LDP) and Hydra Core Vocabularies. It provides examples of modeling an address book container and contacts as LDP resources, supporting common operations like GET, POST and PATCH. It also shows how to describe the application's API using the Hydra Core Vocabulary, including supported classes, operations and documentation. Potential conflicts between LDP and Hydra concepts like containers vs collections and paging are discussed.

1. Describing LDP Applications
with the Hydra Core Vocabulary
Nandana Mihindukulasooriya, and Raúl García-Castro
Ontology Engineering Group (OEG)
Facultad de Informática
Universidad Politécnica de Madrid

2. Linked Data Platform 1.0
2Nandana Mihindukulasooriya, OEG

3. An example application
3Nandana Mihindukulasooriya, OEG
• An address book – for managing contacts
• Contacts
• Create, List, Update, Delete
• User
• Retrieve
Alice
<<user>>
Alice’s
Address Book Alice’s
Contacts

4. Address Book
4Nandana Mihindukulasooriya, OEG
Address Book
Application
Address Book
Client

5. Domain Model
5Nandana Mihindukulasooriya, OEG
AddressBook Contact
•email
•fullName
•telephone
•url
User
•name •title
Schema Restrictions
• Data types
• Cardinalities

6. LDP Model
6Nandana Mihindukulasooriya, OEG
«BasicContainer»
AddressBook
/{personId}/contacts/
«LDPResource»
Contact
ldp:contains
/{personId}/contacts/{contactId}
«LDPResource»
User
/{personId}/
foaf:
primaryTopic
vcard:Email
vcard:Voice
rdfs:Resource
vcard:hasURL
xsd:string
vcard:hasEmail
vcard:hasTelephone
vcard:fn
xsd:string
foaf:name

7. Application
7Nandana Mihindukulasooriya, OEG
Address Book
Application
Address Book
Client

8. LDP Container - GET
8Nandana Mihindukulasooriya, OEG
GET /alice/contacts/ HTTP/1.1
Host: example.org
Accept: text/turtle
HTTP/1.1 200 OK
Content-Type: text/turtle; charset=UTF-8
Link: <http://www.w3.org/ns/ldp#BasicContainer>; rel='type',
<http://www.w3.org/ns/ldp#Resource>; rel='type’
ETag: W/'123456711'
Allow: OPTIONS, HEAD, GET, POST
Accept-Post: text/turtle, application/ld+json
Content-Length: 250
@prefix ldp: <http://www.w3.org/ns/ldp#> .
@prefix dc: <http://purl.org/dc/terms/> .
@prefix dc: <http://example.org/vocab#> .
<http://example.org/contacts/> a ex:AddressBook, ldp:BasicContainer;
foaf:primaryTopic <http://example.org/alice>;
ldp:contains <bob>, <jim> .

9. LDP Container - GET
9Nandana Mihindukulasooriya, OEG
GET /alice/contacts/ HTTP/1.1
Host: example.org
Accept: text/turtle
HTTP/1.1 200 OK
Content-Type: text/turtle; charset=UTF-8
Link: <http://www.w3.org/ns/ldp#BasicContainer>; rel='type',
<http://www.w3.org/ns/ldp#Resource>; rel='type’
ETag: W/'123456711'
Allow: OPTIONS, HEAD, GET, POST
Accept-Post: text/turtle
Content-Length: 250
@prefix ldp: <http://www.w3.org/ns/ldp#> .
@prefix dc: <http://purl.org/dc/terms/> .
@prefix dc: <http://example.org/vocab#> .
<http://example.org/contacts/> a ex:AddressBook, ldp:BasicContainer;
foaf:primaryTopic <http://example.org/alice>;
ldp:contains <bob>, <jim> .
supports LDP Basic Container interactions

10. LDP Container - GET
10Nandana Mihindukulasooriya, OEG
GET /alice/contacts/ HTTP/1.1
Host: example.org
Accept: text/turtle
HTTP/1.1 200 OK
Content-Type: text/turtle; charset=UTF-8
Link: <http://www.w3.org/ns/ldp#BasicContainer>; rel='type',
<http://www.w3.org/ns/ldp#Resource>; rel='type’
ETag: W/'123456711'
Allow: OPTIONS, HEAD, GET, POST
Accept-Post: text/turtle, application/ld+json
Content-Length: 250
@prefix ldp: <http://www.w3.org/ns/ldp#> .
@prefix dc: <http://purl.org/dc/terms/> .
@prefix dc: <http://example.org/vocab#> .
<http://example.org/contacts/> a ex:AddressBook, ldp:BasicContainer;
foaf:primaryTopic <http://example.org/alice>;
ldp:contains <bob>, <jim> .
supports the mentioned HTTP operations on this resource

11. LDP Container - GET
11Nandana Mihindukulasooriya, OEG
GET /alice/contacts/ HTTP/1.1
Host: example.org
Accept: text/turtle
HTTP/1.1 200 OK
Content-Type: text/turtle; charset=UTF-8
Link: <http://www.w3.org/ns/ldp#BasicContainer>; rel='type',
<http://www.w3.org/ns/ldp#Resource>; rel='type’
ETag: W/'123456711'
Allow: OPTIONS, HEAD, GET, POST
Accept-Post: text/turtle, application/ld+json
Content-Length: 250
@prefix ldp: <http://www.w3.org/ns/ldp#> .
@prefix dc: <http://purl.org/dc/terms/> .
@prefix dc: <http://example.org/vocab#> .
<http://example.org/contacts/> a ex:AddressBook, ldp:BasicContainer;
foaf:primaryTopic <http://example.org/alice>;
ldp:contains <bob>, <jim> .
Turtle and JSON-LD media types are accepted on POST

12. 12Nandana Mihindukulasooriya, OEG
http://kristenbloggen.net/wp-content/uploads/good.jpg

13. LDP Container - POST
13Nandana Mihindukulasooriya, OEG
POST /nandana/contacts/ HTTP/1.1
Host: example.org
Slug: jane
Link: <http://www.w3.org/ns/ldp#Resource>; rel='type'
Content-Type: text/turtle
@prefix vcard: <http://www.w3.org/2006/vcard/ns#> .
< > a ex:Contact, vcard:Individual;
vcard:hasURL <http://example.org/jane#me> ;
vcard:hasEmail <mailto:jane@example.com>;
vcard:fn “Jane Doe";
vcard:hasTelephone [ a vcard:Home, vcard:Voice;
vcard:hasValue <tel:+34655555555> ] .
expected Input
(vocabulary,
cardinalities)
supports Slug header

14. LDP Container - GET
14Nandana Mihindukulasooriya, OEG
GET /alice/contacts/ HTTP/1.1
Host: example.org
Accept: text/turtle
HTTP/1.1 200 OK
Content-Type: text/turtle; charset=UTF-8
Link: <http://www.w3.org/ns/ldp#BasicContainer>; rel='type',
<http://www.w3.org/ns/ldp#Resource>; rel='type’
ETag: W/'123456711'
Allow: OPTIONS, HEAD, GET, POST
Accept-Post: text/turtle, application/ld+json
Accept-Patch: text/ldpatch
Content-Length: 250
@prefix ldp: <http://www.w3.org/ns/ldp#> .
@prefix dc: <http://purl.org/dc/terms/> .
@prefix dc: <http://example.org/vocab#> .
<http://example.org/contacts/> a ex:AddressBook, ldp:BasicContainer;
foaf:primaryTopic <http://example.org/alice>;
ldp:contains <bob>, <jim> .
Hypermedia controls

15. 15Nandana Mihindukulasooriya, OEG
http://www.teresacommunicates.com/wp-content/uploads/2014/01/i-can-do-this.jpg

16. LDP Container - GET
16Nandana Mihindukulasooriya, OEG
GET /alice/contacts/ HTTP/1.1
Host: example.org
Accept: application/vnd.ldp.addressbook+turtle
HTTP/1.1 200 OK
Content-Type: application/vnd.ldp.addressbook+turtle; charset=UTF-8
Link: <http://www.w3.org/ns/ldp#BasicContainer>; rel='type',
<http://www.w3.org/ns/ldp#Resource>; rel='type’
ETag: W/'123456711'
Allow: OPTIONS, HEAD, GET, POST
Accept-Post: application/vnd.ldp.contact+turtle;
Accept-Patch: text/ldpatch
Content-Length: 250
@prefix ldp: <http://xmlns.com/foaf/0.1/> .
@prefix dc: <http://purl.org/dc/terms/> .
@prefix dc: <http://example.org/vocab#> .
<http://example.org/contacts/> a ex:AddressBook, ldp:BasicContainer;
foaf:primaryTopic <http://example.org/alice>;
ldp:contains <bob>, <jim> .

17. LDP Container V1 - GET
17Nandana Mihindukulasooriya, OEG
GET /alice/contacts/ HTTP/1.1
Host: example.org
Accept: application/vnd.ldp.addressbook.v1+turtle
HTTP/1.1 200 OK
Content-Type: application/vnd.ldp.addressbook.v1+turtle; charset=UTF-8
Link: <http://www.w3.org/ns/ldp#BasicContainer>; rel='type',
<http://www.w3.org/ns/ldp#Resource>; rel='type’
ETag: W/'123456711'
Allow: OPTIONS, HEAD, GET, POST
Accept-Post: application/vnd.ldp.contact.v1+turtle;
Accept-Patch: text/ldpatch
Content-Length: 250
@prefix ldp: <http://xmlns.com/foaf/0.1/> .
@prefix dc: <http://purl.org/dc/terms/> .
@prefix dc: <http://example.org/vocab#> .
<http://example.org/contacts/> a ex:AddressBook, ldp:BasicContainer;
foaf:primaryTopic <http://example.org/alice>;
ldp:contains <bob>, <jim> .

18. 18Nandana Mihindukulasooriya, OEG

19. Hydra Core Vocabulary
19Nandana Mihindukulasooriya, OEG

20. LDP Container – GET /w Hydra API Link relation
20Nandana Mihindukulasooriya, OEG
HTTP/1.1 200 OK
Content-Type: text/turtle; charset=UTF-8
Link: <http://www.w3.org/ns/ldp#BasicContainer>; rel=“type”,
<http://www.w3.org/ns/ldp#Resource>; rel=“type”
Link: <http://example.com/doc/>;
rel="http://www.w3.org/ns/hydra/core#apiDocumentation"
ETag: W/'123456711'
Allow: OPTIONS, HEAD, GET, POST
Accept-Post: text/turtle, application/ld+json
Accept-Patch: text/ldpatch
Content-Length: 250
@prefix ldp: <http://www.w3.org/ns/ldp#> .
@prefix dc: <http://purl.org/dc/terms/> .
<http://example.org/contacts/> a ldp:BasicContainer;
foaf:primaryTopic <http://example.org/alice>;
ldp:contains <bob>, <jim> .

21. API Documentation
21Nandana Mihindukulasooriya, OEG
{
"@context": [
"http://www.w3.org/ns/hydra/context.jsonld",
{…}
],
"@id": "http://example.org/docs/",
"@type": "ApiDocumentation",
"title": "LDP Address Book API",
"entrypoint": "http://example.org/contacts/",
"supportedClass": [
{
"@id": "ex:AddressBook",
"@type": "hydra:Class",
"subClassOf": "ldp:BasicContainer",
"label": "An example address book",
…
},
….
],
…

22. API Documentation
22Nandana Mihindukulasooriya, OEG
{
"supportedClass": [
{
"@id": "ex:AddressBook",
"@type": "hydra:Class",
"subClassOf": "ldp:BasicContainer",
"label": "An example address book",
"supportedOperation": [
{
"@id": "_:create_new_contact",
"@type": "hydra:Operation",
"method": "POST",
"label": "creates a new contact in the address book",
"description": null,
"expects": “ex:Contact",
"returns": null,
"statusCodes": [
…
]
},

23. API Documentation
23Nandana Mihindukulasooriya, OEG
{
"supportedClass": [
{
"@id": "ex:AddressBook",
"@type": "hydra:Class",
"subClassOf": "ldp:BasicContainer",
"label": "An example address book",
"supportedOperation": [
{
"@id": "_:create_new_contact",
"@type": "hydra:Operation",
"method": "POST",
"label": "creates a new contact in the address book",
"description": null,
"expects": “ex:Contact",
"returns": null,
"statusCodes": [
…
]
},

24. API Documentation
24Nandana Mihindukulasooriya, OEG
{
"supportedClass": [
…..
{
"@id": "ex:Contact",
"@type": "hydra:Class",
"subClassOf": “vcard:Individual",
"label": “A contact",
" supportedProperty": [
{
"property": “vcard:hasEmail",
"hydra:title": “Email”,
"hydra:description": “Email of the contact",
"required": true,
"readable": true,
"writable": false,
},

25. Potential Conflicts
• Similar concepts in LDP and Hydra
• LDP Containers Vs Hydra Collections
• LDP Paging Vs Hydra Paged Collections
25Nandana Mihindukulasooriya, OEG

26. Collections vs Containers
26Nandana Mihindukulasooriya, OEG
@prefix hydra: <http://www.w3.org/ns/hydra/core#>
<http://example.org/alice/contacts> a hydra:Collection ;
hydra:member <http://example.org/alice/contacts/bob>,
<http://example.org/alice/contacts/jane> .
• Hydra Collection
• LDP Container
@prefix ldp: <http://www.w3.org/ns/ldp#> .
<http://example.org/alice/contacts> a ldp:BasicContainer ;
ldp:contains <http://example.org/alice/contacts/bob>,
<http://example.org/alice/contacts/jane> .

27. Hydra collection as an LDP Direct Container
27Nandana Mihindukulasooriya, OEG
@prefix hydra: <http://www.w3.org/ns/hydra/core#> .
@prefix ldp: <http://www.w3.org/ns/ldp#> .
<http://example.org/alice/contacts> a hydra:Collection, ldp:DirectContainer;
ldp:membershipResource <>;
ldp:hasMemberRelation hydra:member;
ldp:contains <http://example.org/alice/contacts/bob>,
<http://example.org/alice/contacts/jane> ;
hydra:member <http://example.org/alice/contacts/bob>,
<http://example.org/alice/contacts/jane> ;

28. LDP Paging
28Nandana Mihindukulasooriya, OEG
GET /nandana?page2 HTTP/1.1
Host: example.org
Accept: text/turtle
Prefer: return=representation; max-triple-count="500"
HTTP/1.1 200 OK
Content-Type: text/turtle
ETag: "_87e52ce291112"
Link: <http://www.w3.org/ns/ldp#Resource>; rel="type",
<http://www.w3.org/ns/ldp#Page>; rel="type"
Link: <http://example.org/alice/contacts?p=3>; rel="next"
Link: <http://example.org/alice/contacts>; rel="canonical"; etag="_87e5"
Link: <http://example.org/alice/contacts?page1>; rel="first"
Link: <http://example.org/alice/contacts?p=4>; rel="last"
Link: <http://example.org/alice/contacts?page1>; rel="prev"
Allow: GET,OPTIONS,HEAD

29. Hydra PagedCollection
29Nandana Mihindukulasooriya, OEG
@prefix hydra: <http://www.w3.org/ns/hydra/core#> .
@prefix ldp: <http://www.w3.org/ns/ldp#> .
{
"@context": "http://www.w3.org/ns/hydra/context.jsonld",
"@id": "http://example.org/alice/contacts?page=3",
"@type": "PagedCollection",
"totalItems": “50",
"itemsPerPage": "10",
"firstPage": "http://example.org/alice/contacts?page=1",
"nextPage": " http://example.org/alice/contacts?page=4",
"previousPage": "http://example.org/alice/contacts?page=2",
"lastPage": "http://example.org/alice/contacts?page=5",
"member": [
... the members of this PagedCollection ...
]
}

30. Conclusions
• LDP needs mechanisms for vocabulary and
affordance discovery
• Hydra Core vocabulary can be used describe LDP
application
• Why not just Hydra?
• There are overlaps in some areas
• Overlaps with the W3C RDF Shapes WG
30Nandana Mihindukulasooriya, OEG