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Martynas Jusevičius edited this page Sep 13, 2019 · 3 revisions

CRUD operations

This section shows a mapping between URIs, HTTP methods and operations.

Method Success Failure Message
GET 200 OK Resource description returned
400 Bad Request Unrecognized parameter name
400 Bad Request Invalid parameter value
404 Not Found Resource not found
406 Not Acceptable Media type not supported
POST 200 OK Dataset appended
400 Bad Request Invalid request body syntax
400 Bad Request Constraint violation
404 Not Found Resource not found
409 Conflict Resource already exists
415 Unsupported Media Type Media type not supported
PUT 200 OK Resource description updated
400 Bad Request Invalid request body syntax
400 Bad Request Constraint violation
404 Not Found Resource not found
409 Conflict Resource description has changed
415 Unsupported Media Type Media type not supported
DELETE 204 No Content Resource deleted
404 Not Found Resource not found

The update is done using SPARQL 1.1 Update command defined by the LDT template's ldt:update property. However, Graph Store Protocol is often more convenient .

Content negotiation is implemented via the Accept request header. All RDF serializations supported by Jena (registered in RDFLanguages) are accepted. A streaming RDF/POST reader is registered as well.

Validation

All incoming RDF is validated using SPIN API against the spin:constraints in the domain ontology. If any constraint is violated, the request is rejected and response with 400 Bad Request status is returned.

The constraints themselves are either ASK (for a simple true/false answer) or CONSTRUCT (for a more detailed violation message) queries. The Data Quality Constraints Library is a useful ontology to import, as it contains some often needed constraints such as a check for missing properties.

Consider the following resource class with a constraint (other properties omitted):

@prefix owl:	<http://www.w3.org/2002/07/owl#> .
@prefix sp:     <http://spinrdf.org/sp#> .
@prefix spin:	<http://spinrdf.org/spin#> .
@prefix dqc:	<http://semwebquality.org/ontologies/dq-constraints#> .

dh:Document a owl:Class ;
    spin:constraint [ a dqc:MissingProperties ;
	    sp:arg1 dh:Document ;
	    sp:arg2 dh:slug
	] .

and the following POST request body:

@prefix dh:	<https://www.w3.org/ns/ldt/document-hierarchy/domain#> .

_:item a dh:Document .

The request will be rejected, as the _:item resource has dh:Document type but does not have the dh:slug property required by the SPIN constraint.

Skolemization

Blank nodes in POST request payload are skolemized, i.e. renamed into URI resources. URI template is defined for a class using ldt:path, which allows to use resource property values in the URI and navigating to related resource descriptions using a property path-like syntax.

Resources that are do not have foaf:Document type (e.g. denoting physical object such as foaf:Person instance or abstract concept such as skos:Concept terms) should have have different URIs from the documents that are describing them. One simple convention for doing that is to use fragment URIs for them, e.g. by adding #this fragment to the document URI. Another LDT property ldt:fragment can be used to specify that for a class.

After a relative URI is built from the template, it is resolved against the request URI and becomes absolute. Only resources with recognized type classes are skolemized, unmatched bnodes are left untouched.

For example, using http://localhost:8080/items/ as POST request URI, skolemizing the following request body

@prefix dh:	<https://www.w3.org/ns/ldt/document-hierarchy/domain#> .
@prefix foaf:   <http://xmlns.com/foaf/0.1/> .

_:item a dh:Document ;
  foaf:primaryTopic _:thing .
_:thing a a owl:Thing ;
  rdfs:label "I'm a Thing" ;
  foaf:isPrimaryTopicOf _:item .

while processing a LDT ontology with the following triples

dh:Document ldt:path "{primaryTopic.label}" . # property path, using local names only
owl:Thing ldt:path "{label}" .

yields following result which is ready to be stored in the triplestore:

@prefix dh:	<https://www.w3.org/ns/ldt/document-hierarchy/domain#> .
@prefix foaf:   <http://xmlns.com/foaf/0.1/> .

<http://localhost:8080/items/I%27m%20a%20Thing> a dh:Document ;
  foaf:primaryTopic <http://localhost:8080/items/I%27m%20a%20Thing#this> .
<http://localhost:8080/items/I%27m%20a%20Thing#this> a owl:Thing ;
  foaf:isPrimaryTopicOf <http://localhost:8080/items/I%27m%20a%20Thing> .
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