Reading and Searching Resources

In order to get an existing resource, the HTTP method GET has to be used. The request has to be sent to the Knora server using the resources path segment (depending on the type of request, this segment has to be exchanged, see below). Reading resources may require authentication since some resources may have restricted viewing permissions.

Get the Representation of a Resource by its IRI

Simple Request of a Resource (full Resource Request)

A resource can be obtained by making a GET request to the API providing its IRI. Because a Knora IRI has the format of a URL, its IRI has to be URL encoded.

In order to get the resource with the IRI http://rdfh.ch/c5058f3a (an incunabula book contained in the test data), make a HTTP GET request to the resources route (path segment resources in the API call) and append the URL encoded IRI:

HTTP GET to http://host/v1/resources/http%3A%2F%2Frdfh.ch%2Fc5058f3a

More formalized, the URL looks like this:

HTTP GET to http://host/v1/resources/resourceIRI

As an answer, the client receives a JSON that represents the requested resource. It has the following members:

status: The Knora status code, 0 if everything went well
userdata: Data about the user that made the request
resinfo: Data describing the requested resource and its class
resdata: Short information about the resource and its class (including information about the given user's permissions on the resource)
incoming: Resources pointing to the requested resource
props: Properties of the requested resource.

For a complete and more formalized description of a full resource request, look at the TypeScript interface resourceFullResponse in the module resourceResponseFormats.

Provide Request Parameters

To make a request more specific, the following parameters can be appended to the URL (http://www.knora.org/resources/resourceIRI?param1=value1&param2=value2):

reqtype=info|context|rights: Specifies the type of request.
- Setting the parameter's to value info returns short information about the requested resource (contains only resinfo and no properties, see TypeScript interface resourceInfoResponse in module resourceResponseFormats).
- Setting the parameter's value to context returns context information (resource_context) about the requested resource: Either the dependent parts of a compound resource (e.g. pages of a book) or the parent resource of a dependent resource (e.g. the book a pages belongs to). By default, a context query does not return information about the requested resource itself, but only about its context (see TypeScript interface resourceContextResponse in module resourceResponseFormats). See below how to get additional information about the resource.
- The parameter rights returns only the given user's permissions on the requested resource (see TypeScript interface resourceRightsResponse in module resourceResponseFormats).
resinfo=true: Can be used in combination with reqtype=context: If set, resinfo is added to the response representing information about the requested resource (complementary to its context), see TypeScript interface resourceContextResponse in module resourceResponseFormats.

Obtain an HTML Representation of a Resource

In order to get an HTML representation of a resource (not a JSON), the path segment resources.html can be used:

HTTP GET to http://host/v1/resources.html/resourceIRI?reqtype=properties

The request returns the properties of the requested resource as an HTML document.

Get only the Properties belonging to a Resource

In order to get only the properties of a resource without any other information, the path segment properties can be used:

HTTP GET to http://host/v1/properties/resourceIRI

The JSON contains just the member properties representing the requested resource's properties (see TypeScript interface resourcePropertiesResponse in module resourceResponseFormats).

Get Information about a Resource Class

Get a Resource Class by its IRI

In order to get information about a resource class, the path segment resourcetypes can be used. Append the IRI of the resource class to the URL (e.g. http://www.knora.org/ontology/0803/incunabula#book).

HTTP GET to http://host/v1/resourcetypes/resourceClassIRI

In the JSON, the information about the resource class and all the property types that it may have are returned. None of these are actual instances of a property, but only types (see TypeScript interface resourceTypeResponse in module resourceResponseFormats).

Get all the Property Types of a Resource Class or a Vocabulary

To get a list of all the available property types, the path segment propertylists can be used. It can be restricted to a certain vocbulary using the parameter vocabulary or to a certain resource class using the parameter restype.

# returns all the property types for incunabula:page
HTTP GET to http://host/v1/propertylists?restype=resourceClassIRI

# returns all the property types for the incunabula vocabulary
HTTP GET to http://host/v1/propertylists?vocabulary=vocabularyIRI

Both of these queries return a list of property types. The default value for the parameter vocabulary is 0 and means that the resource classes from all the available vocabularies are returned. See TypeScript interface propertyTypesInResourceClassResponse in module resourceResponseFormats.

Get the Resource Classes of a Vocabulary

Resource classes and property types are organized in (project specific) name spaces, so called vocabularies. In order to get all the resource classes defined for a specific vocabulary (e.g. incunabula), the parameter vocabulary has to be used and assigned the vocabulary's IRI:

HTTP GET to http://host/v1/resourcetypes?vocabulary=vocabularyIRI

This returns all the resource classes defined for the specified vocabulary and their property types. The default value for the parameter vocabulary is 0 and means that the resource classes from all the available vocabularies are returned. See TypeScript interface resourceTypesInVocabularyResponse in module resourceResponseFormats.

Get all the Vocabularies

To get a list of all available vocabularies, the path segment vocabularies can be used:

HTTP GET to http://host/v1/vocabularies

The response will list all the available vocabularies. See TypeScript interface vocabularyResponse in module resourceResponseFormats.

Search for Resources

Search for Resources by their Label

This is a simplified way for searching for resources just by their label. Search by label automatically adds Lucene operators, search strings are expected not to contain any characters with a special meaning in Lucene Query Parser syntax.

It is a simple string-based method:

HTTP GET to http://host/v1/resources?searchstr=searchValue

Additionally, the following parameters can be appended to the URL (search value is Zeitglöcklein):

restype_id=resourceClassIRI: This restricts the search to resources of the specified class (subclasses of that class will also match). -1 is the default value and means no restriction to a specific class. If a resource class IRI is specified, it has to be URL encoded (e.g. http://www.knora.org/v1/resources?searchstr=Zeitgl%C3%B6cklein&restype_id=http%3A%2F%2Fwww.knora.org%2Fontology%2Fincunabula%23book).
numprops=Integer: Specifies the number of properties returned for each resource that was found (sorted by GUI order), e.g. http://www.knora.org/v1/resources?searchstr=Zeitgl%C3%B6cklein&numprops=4.
limit=Integer: Limits the amount of results returned (e.g. http://www.knora.org/v1/resources?searchstr=Zeitgl%C3%B6cklein&limit=1).

The response lists the resources that matched the search criteria (see TypeScript interface resourceLabelSearchResponse in module resourceResponseFormats).

Fulltext Search

Knora offers a fulltext search that searches through all textual representations of values. The search terms have to be URL encoded. Fulltext search supports the Lucene Query Parser syntax. Note that Lucene's default operator is a logical OR when submitting several search terms.

HTTP GET to http://host/v1/search/searchValue?searchtype=fulltext[&filter_by_restype=resourceClassIRI]
[&filter_by_project=projectIRI][&show_nrows=Integer]{[&start_at=Integer]

The parameter searchtype is required and has to be set to fulltext. Additionally, these parameters can be set:

filter_by_restype=resourceClassIRI: restricts the search to resources of the specified resource class (subclasses of that class will also match).
filter_by_project=projectIRI: restricts the search to resources of the specified project.
show_nrows=Integer: Indicates how many reults should be presented on one page. If omitted, the default value 25 is used.
start_at=Integer: Used to enable paging and go through all the results request by request.

The response presents the retrieved resources (according to show_nrows and start_at) and information about paging. If not all resources could be presented on one page (nhits is greater than shown_nrows), the next page can be requested (by increasing start_at by the number of show_nrows). You can simply go through the elements of paging to request the single pages one by one. See TypeScript interface searchResponse in module searchResponseFormats.

Extended Search for Resources

HTTP GET to http://host/v1/search/?searchtype=extended
[&filter_by_restype=resourceClassIRI][&filter_by_project=projectIRI][&filter_by_owner=userIRI]
(&property_id=propertyTypeIRI&compop=comparisonOperator&searchval=searchValue)+
[&show_nrows=Integer][&start_at=Integer]

The parameter searchtype is required and has to be set to extended. An extended search requires at least one set of parameters consisting of:

property_id=propertyTypeIRI: the property the resource has to have (subproperties of that property will also match).
compop=comparisonOperator: the comparison operator to be used to match between the resource's property value and the search term.
searchval=searchTerm: the search value to look for.

You can also provide several of these sets to make your query more specific.

The following table indicates the possible combinations of value types and comparison operators:

Value Type	Comparison Operator
Date Value	EQ, !EQ, GT, GT_EQ, LT, LT_EQ, EXISTS
Integer Value	EQ, !EQ, GT, GT_EQ, LT, LT_EQ, EXISTS
Float Value	EQ, !EQ, GT, GT_EQ, LT, LT_EQ, EXISTS
Text Value	MATCH_BOOLEAN, MATCH, EQ, !EQ, LIKE, !LIKE, EXISTS
Geometry Value	EXISTS
Geoname Value	EQ, EXISTS
URI Value	EQ, EXISTS
Resource Pointer	EQ, EXISTS
Color Value	EQ, EXISTS
List Value	EQ, EXISTS
Boolean Value	EQ, !EQ, EXISTS

Explanation of the comparison operators:

EQ (equal): checks if a resource's value equals the search value. In case of a text value type, it checks for identity of the strings compared. In case of a date value type, equality is given if the dates overlap in any way. Since dates are internally always treated as periods, equality is given if a date value's period ends after or equals the start of the defined period and a date value's period starts before or equals the end of the defined period.
!EQ (not equal): checks if a resource's value does not equal the search value. In case of a text value type, it checks if the compared strings are different. In case of a date value type, inequality is given if the dates do not overlap in any way, meaning that a date starts after the end of the defined period or ends before the beginning of the defined period (dates are internally always treated as periods, see above).
GT (greater than): checks if a resource's value is greater than the search value. In case of a date value type, it assures that a period begins after the indicated period's end.
GT_EQ (greater than or equal): checks if a resource's value equals or is greater than the search value. In case of a date value type, it assures that the periods overlap in any way (see EQ) or that the period starts after the indicated period's end (see GT).
LT (less than): checks if a resource's value is lower than the search value. In case of a date value type, it assures that a period ends before the indicated period's start.
LT_EQ (less than or equal): checks if a resource's value equals or is lower than the search value. In case of a date value type, it assures that the periods overlap in any way (see EQ) or that the period ends before the indicated period's start (see LT).
EXISTS: checks if an instance of the indicated property type exists for a resource. Please always provide an empty search value when using EXISTS: "searchval=". Otherwise, the query syntax rules would be violated.
MATCH: checks if a resource's text value matches the search value, see Lucene Query Parser Syntax.
LIKE: checks if the search value is contained in a resource's text value using the SPARQL REGEX function, thus supporting regular expressions.
!LIKE (not like): checks if the search value is not contained in a resource's text value using the SPARQL REGEX function, thus supporting regular expressions.
MATCH_BOOLEAN: checks if a resource's text value matches the provided list of positive (exist) and negative (do not exist) terms. The list takes this form: ([+-]term\s)+.

Additionally, these parameters can be set:

filter_by_restype=resourceClassIRI: restricts the search to resources of the specified resource class (subclasses of that class will also match).
filter_by_project=projectIRI: restricts the search to resources of the specified project.
filter_by_owner: restricts the search to resources owned by the specified user.
show_nrows=Integer: Indicates how many reults should be presented on one page. If omitted, the default value 25 is used.
start_at=Integer: Used to enable paging and go through all the results request by request.

Some sample searches:

http://localhost:3333/v1/search/?searchtype=extended&filter_by_restype=http%3A%2F%2Fwww.knora.org%2Fontology%2Fincunabula%23book&property_id=http%3A%2F%2Fwww.knora.org%2Fontology%2Fincunabula%23title&compop=!EQ&searchval=Zeitgl%C3%B6cklein%20des%20Lebens%20und%20Leidens%20Christi: searches for books that have a title that does not equal "Zeitglöcklein des Lebens und Leidens Christi".
http://www.knora.org/v1/search/?searchtype=extended&filter_by_restype=http%3A%2F%2Fwww.knora.org%2Fontology%2Fincunabula%23book&property_id=http%3A%2F%2Fwww.knora.org%2Fontology%2Fincunabula%23title&compop=MATCH&searchval=Zeitgl%C3%B6cklein&property_id=http%3A%2F%2Fwww.knora.org%2Fontology%2Fincunabula%23pubdate&compop=EQ&searchval=JULIAN:1490: searches for resources of type incunabula:book whose titles match "Zeitglöcklein" and were published in the year 1490 (according to the Julian calendar).

The response presents the retrieved resources (according to show_nrows and start_at) and information about paging. If not all resources could be presented on one page (nhits is greater than shown_nrows), the next page can be requested (by increasing start_at by the number of show_nrows). You can simply go through the elements of paging to request the single pages one by one. See the TypeScript interface searchResponse in module searchResponseFormats.

Get a Graph of Resources

The path segment graphdata returns a graph of resources that are reachable via links to or from an initial resource.

HTTP GET to http://host/v1/graphdata/resourceIRI?depth=Integer

The parameter depth specifies the maximum depth of the graph, and defaults to 4. If depth is 1, the operation will return only the initial resource and any resources that are directly linked to or from it.

The graph includes any link that is a subproperty of knora-base:hasLinkTo, except for links that are subproperties of knora-base:isPartOf. Specifically, if resource R1 has a link that is a subproperty of knora-base:isPartOf pointing to resource R2, no link from R1 to R2 is included in the graph.

The response represents the graph as a list of nodes (resources) and a list of edges (links). For details, see the TypeScript interface graphDataResponse in module graphDataResponseFormats.

Get Hierarchical Lists

The knora-base ontology allows for the definition of hierarchical lists. These can be queried by providing the IRI of the root node. Selections are hierarchical list that are just one level deep. Internally, they are represented as hierarchical lists.

You can get a hierarchical by using the path segment hlists and appending the hierarchical list's IRI (URL encoded):

HTTP GET to http://host/v1/hlists/rootNodeIRI

The response shows all of the list nodes that are element of the requested hierarchical list as a tree structure. See TypeScript interface hierarchicalListResponse in module hierarchicalListResponseFormats.

For each node, the full path leading to it from the top level can be requested by making a query providing the node's IRI and setting the param reqtype=node:

HTTP GET to http://host/v1/hlists/nodeIri?reqtype=node

The response presents the full path to the current node. See the TypeScript interface nodePathResponse in module hierarchicalListResponseFormats.

Last update: 2022-06-22