Describing LDP Applications with the Hydra Core Vocabulary

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
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Address Book
Application
Address Book
Client

5. Domain Model
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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> .

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19. Hydra Core Vocabulary
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20. LDP Container – GET /w Hydra API Link relation
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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
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26. Collections vs Containers
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@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
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@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
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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
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@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