OSLC Core Query Syntax DRAFT
By: The
OSLC Core Workgroup
Overview
This document defines a standard set of OSLC query parameters that other OSLC domain specifications
MAY use to query resources.
Graph Patterns
The OSLC standard query parameters define
graph patterns that are matched against the resources managed by the service, which we view as comprising an RDF graph. The pattern matching process begins at some
starting subject resource and matches a set of triples in the RDF graph. The starting subject resources used for pattern matching are determined by the the Query Capability. A Query Capability defines a starting subject resource, namely the base URI itself. The result of the query is the set of all triples matched by the pattern, beginning the matching processing with the starting subject resource defined by the Query Capability.
The full graph pattern defined by the query parameters is composed of two kinds of graph pattern, which we refer to as
property tree patterns and
member list patterns. These patterns MAY be used individually or MAY be combined in a single query, but one or the other
MUST be present. The result of matching the full graph pattern is the union of the results of matching each kind of pattern.
Property Tree Patterns
A property tree pattern is defined by the presence of the
oslc.properties
query parameter. In RDF, the data model of a resource is viewed as consisting of a set of properties of the resource. The values of these properties are either literal values, such as numbers, strings, and dates, or links to other resources, which may have their own properties. Linked resources may link to other resources, and so on, to arbitrary depths. However, the scope of the query is limited to the boundaries of the service as defined by the appropriate domain specification. Properties of linked resources may be viewed as nested properties of the initial resource. The
oslc.properties
query parameter lets you match both the immediate and nested properties of a starting subject resource.
Member List Patterns
A member list pattern is defined by the presence of at least one of the following query parameters:
oslc.where
,
oslc.searchTerms
,
oslc.orderBy
, and
oslc.select
. In this pattern, the starting subject resource is viewed as a container of other resources. The members of the container are defined by one or more multi-valued membership properties of the starting subject resource. The membership properties are given by the the properties described as membership properties (via
oslc:isMemberProperty
) in the Resource Shape of the starting subject resource. The pattern matching process is defined by the following sequence of steps. Default processing is done in steps where the corresponding query parameter is not present:
-
oslc.where
- filter the member list, keeping only those member resources that satisfy the boolean test on the member resource properties
-
oslc.searchTerm
- score each member resource using a full text search on it text-valued properties, and sort them in descending order of score
-
oslc.orderBy
- sort the members using the sort keys, using the full text search score as the primary key
-
oslc.select
- match the immediate and nested properties of the member resources (like in oslc.properties
)
Prefixed Names
In addition to the preceeding query parameters, we also define
oslc.prefix
which is used to define the prefixes for prefixed names that appear in the other query parameters. The
oslc.prefix
query parameter is not itself part of the graph pattern. Other specifications MAY use
oslc.prefix
to define prefixes for prefixed name used other query parameters.
Query Parameters
The query parameters defined here are intended to satsify simple query requirements, and be easy to both use and implement. More complex query requirements should be satisfied using a full query language, e.g. SQL or SPARQL.
This specification formally defines the syntax of the query parameters using
Backus-Naur Form (BNF) and informally illustrates their semantics with simple examples. For a more complete definition of the semantics see
OSLC Simple Query Semantics V1.
The query parameters MAY contain characters that MUST be URL encoded when transmitted in an HTTP request. The examples below show unencoded query parameters for clarity. See
URL Encoding for a further discussion of this topic.
This specification defines the syntax of a set of related query parameters that MAY be used to perform queries. We have adopted a consistent naming convention for these query parameters to identify them as common across all OSLC specifications, namely all query parameter names are prefixed with the characters "
oslc.
" The following sections define these query parameters.
An OSLC domain specification MAY use some or all of these query parameters, and SHOULD use these rather than defining new query parameters that have the same or very similar meanings.
Each of these query parameters SHOULD appear at most once in a query. The behavior is undefined when a query parameter appears more than once.
In the following sections, syntax is formally defined using a common extended form of BNF. Informal definitions and comments are delimited by /* and */.
oslc.where
This query parameter defines part of a member list pattern. If a member list pattern is define but this query parameter is not present then it defaults to the boolean condition
true
, i.e. it matches all members of the member list.
As discussed in the section on
oslc.from
, a resource may have an associated set of related resources defined by one or more membership properties. Service consumers often need to search for subsets of these related resources that satisfy certain conditions. The
oslc.where
query parameter lets you specify the conditions that these related resources must satisfy. It is like the
WHERE
clause of a SQL statement.
For example, suppose that the following URL represents the set of all bug resources managed by a service, and that is has a single membership property,
cm:memberBug
:
http://example.com/bugs
Suppose bug reports have a
dcterms:identifier
property that gives their bug number, e.g.
"4242"
. The following URL filters this set and selects only those bugs that have a
dcterms:identifier
property whose value is
"4242"
:
http://example.com/bugs?oslc.where=dcterms:identifier="4242"
Note that in the preceding query, the
oslc.from
query parameter is absent so it defaults to all the membership properties, and in this case there is only one, namely
cm:memberBug
.
Conditions may use the usual binary comparison operators and be combined using the boolean conjunction operator, "
and
". For example, suppose bugs have
cm:severity
and
dcterms:created
properties. The following example finds high severity bugs created after April 1, 2010:
http://example.com/bugs?oslc.where=cm:severity="high" and dcterms:created>"2010-04-01"
The following URL illustrates the use of nested properties. It finds the set of bugs created by John Smith:
http://example.com/bugs?oslc.where=dcterms:creator{foaf:givenName="John" and foaf:familyName="Smith"}
Syntax
The syntax of the
oslc.where
query parameter is defined by the
oslc_where
term in the following BNF grammar:
oslc_where ::= "oslc.where=" compound_term
compound_term ::= simple_term (space? boolean_op space? simple_term)*
simple_term ::= term | scoped_term
space ::= " " /* a space character */
boolean_op ::= "and"
term ::= identifier_wc comparison_op value | identifier_wc space in_op space? in_val
scoped_term ::= identifier_wc "{" compound_term "}"
identifier_wc ::= identifier | wildcard
comparison_op ::= "=" | "!=" | "<" | ">" | "<=" | ">="
in_op ::= "in"
in_val ::= "[" value ("," value)* "]"
value ::= uri_ref_esc | literal_value
literal_value ::= boolean | decimal | string_esc (LANGTAG | ("^^" PrefixedName))?
boolean ::= "true" | "false"
decimal ::= /* see "XML Schema Part 2: Datatypes Second Edition", http://www.w3.org/TR/xmlschema-2/ */
string_esc ::= /* a string enclosed in double quotes, with certain characters escaped. See below. */
LANGTAG ::= /* see "SPARQL Query Lanaguage for RDF", http://www.w3.org/TR/rdf-sparql-query/#rLANGTAG */
boolean_op
The
boolean_op
term represents a boolean operation that lets you combine simple boolean expressions to form a compound boolean expression.
The only boolean operation allowed is "
and
" which represents conjunction. The boolean operator "
or
" for disjunction is not allowed in the interests of keeping the syntax simple. The effect of "
or
" in the simple case of testing a property for equality with one of several values can be achieved through the use of the "
in
" operator. For example, the following query finds bugs with severity "
high
" or "
medium
":
http://example.com/bugs?oslc.where=cm:severity in ["high","medium"]
space
The
space
term represents a single space character. A space character
MAY be used to delimit the
binary_op
term in the
compound_term
term to improve readability.
comparison_op
The
comparison_op
term represents one of the following binary comparison operators:
= |
test for equality |
= |
test for inequality |
< |
test less-than |
> |
test greater-than |
<= |
test less-than or equal |
>= |
test greater-than or equal |
in_op
The
in_op
term represents the operator "
in
" which is a test for equality to any of the values in a list. The list is a comma-separated sequence of values, enclosed in square brackets, whose syntax is defined by the term
in_val
.
value
The
value
term represents either a URI reference (
uri_ref_esc
) or a literal value (
literal_value
).
literal_value
The
literal_value
term represents either a plain literal or a typed literal.
A plain literal is a quoted string (
string_esc
), optionally followed by a language tag (
LANGTAG
). For example,
"Bonjour"@fr
is a plain literal with a language tag for French. If the range of a property is National Language strings and no language tag is provided in a literal value, then the service
SHOULD infer the language tag from the HTTP request or provide a default value.
A typed literal is formed by suffixing a quoted string (
string_esc
) with "^^" followed by the prefixed name (
PrefixedName
) of a datatype URI. If the range of a property includes literal values from more than one datatype, then a typed literal
MUST be used in order to avoid ambiguity. Otherwise a plain literal
MAY be used and the service
SHOULD infer the datatype.
The terms
boolean
and
decimal
are short forms for typed literals. For example,
true
is a short form for
"true"^^xsd:boolean
,
42
is a short form for
"42"^^xsd:integer
and
3.14159
is a short form for
"3.14159"^^xsd:decimal
.
decimal
The
decimal
term represents a
decimal number as defined in
XML Schema Part 2: Datatypes Second Edition. As mentioned above, this term is a short form for typed literals whose datatype URIs are either
xsd:integer
or
xsd:decimal
. An integer literal value is a special case of a decimal literal value, namely one in which the decimal point is omitted from the lexical representation. For example,
42
is a valid decimal number which happens also to be a valid integer and so it is a short form for the typed literal
"42"^^xsd:integer
.
string_esc
The
string_esc
term represents an arbritrary sequence of characters. The sequence of characters is enclosed in double quote (") characters. Therefore, the double quote character itself
MUST be escaped. All occurances of the double quote character in the string
MUST be replaced by the sequence \" and all occurances of the backslash character (\)
MUST be replaced by the sequence \\. This escaping
MUST be undone to give the actual value of the string.
oslc.searchTerms
This query parameter defines part of a member list pattern. If a member list pattern is defined but this query parameter is not present then the matching process assigns an effective score of 0 to each member of the list and does
NOT change the order of the member list
Resource properties often contain text so it is useful to search for resources that contain specified terms. The
oslc.searchTerms
query parameter lets you perform a
full text search on a set of resources. In a full text search, each resource is matched against the list of search terms and assigned a numeric score. A high score indicates a good match. The matching resources are returned in the response, sorted by the score in descending order. Each resource that is returned in the response is annoted with a special property,
oslc:score
, that gives its match score.
An OSLC domain specification that supports full text search
SHOULD specify which resource properties are indexed so that search results are consistent across implementations.
When
oslc.searchTerms
is used in the request, each matching resource (hit) in the response MAY contain an
oslc:score
property. Note that
oslc:score
is not purely a property of the resource since it also depends on the search terms. It is therefore a pseudo-property whose validity is limited to the HTTP response.
The
oslc:score
property
MUST be a non-negative number and
SHOULD be in the range from 0-100. Results
MUST be ordered with the entry with the largest
oslc:score
occuring first.
The
oslc.orderBy
query parameter
MAY be used with
oslc.searchTerms
. When
oslc.orderBy
is used with
oslc.searchTerms
the result
MUST be first sorted in descending order by the
oslc:score
pseudo-property, and then by the other sort keys specified in
oslc.orderBy
. This behavior is like prepending the list of sort keys specified in
oslc.orderBy
with the key
-oslc:score
. However, the pseudo-property
oslc:score
MUST NOT appear explicitly in
oslc.orderBy
.
The
oslc.where
query parameter
MAY be used with
oslc.searchTerms
. When
oslc.where
is used with
oslc.searchTerms
then the set of resources searched for matches
MUST be restricted to only those resources that satisfy the conditions in
oslc.where
. For example, the following query returns the top 10 high severity bugs that deal with database performance:
http://example.com/bugs?oslc.where=cm:severity="high"&oslc.limit=10&oslc.searchTerms="database","performance"
Syntax
The syntax of the
oslc.searchTerms
query parameter is defined by the
oslc_searchTerms
terms in the following BNF grammar:
oslc_searchTerms ::= "oslc.searchTerms=" search_terms
search_terms ::= string_esc (, string_esc)*
oslc.orderBy
This query parameter defines part of a member list pattern. If a member list pattern is define but this query parameter is not present then there are no sort keys and the matching process does
NOT change the order of the member list.
The
oslc.orderBy
query parameter lets you sort the result set. It is like the
ORDER BY
clause of a SQL statement.
You can specify a list of one or more immediate or nested properties of the resources in the member list, and a sort direction for each where "
+
" means ascending order and "
-"
means descending order. The following example sorts the high severity bugs by the family and given names of the creator, with most recently created first:
http://example.com/bugs?oslc.orderBy=dcterms:creator{+foaf:familyName,+foaf:givenName},-dcterms:created
&oslc.where=cm:severity="high"
The properties in the
oslc.orderBy
list are sort keys. The member list is sorted by the sort keys, in the indicated direction. The sorting order of the property values
MUST be the same as that used for evaluating the binary comparison operators in the
oslc.where
query parameter.
Each sort key
SHOULD be the name of a single-valued property of the each resource in the result set. The sorting behavior is undefined if the sort key properties are not single-valued.
Syntax
The syntax of the
oslc.orderBy
query parameter is defined by the
oslc_orderBy
term in the following BNF grammar:
oslc_orderBy ::= "oslc.orderBy=" sort_terms
sort_terms ::= sort_term ("," sort_term)*
sort_term ::= scoped_sort_terms | ("+" | "-") identifier
scoped_sort_terms ::= identifier "{" sort_terms "}"
positiveInteger
The
positiveInteger
term represents a
positive integer value (reference: XSD Datatypes).
oslc.select
This query parameter defines part of a member list pattern. If a member list pattern is defined but this query parameter is not present then the matching process does
NOT match any properties of the resources in the member list.
The
oslc.select
query parameter lets you specify which immediate and nested properties of the resources in the member list to match. It is like the
SELECT
clause of a SQL statement.
The syntax of the
oslc.select
query parameter is the same as that of the
oslc.properties
query parameter. However, the property names that appear in the
oslc.select
query parameter are those that belong to the resources in the member list as opposed to those that belong to the starting subject resource.
For example, the following URL finds the high severity bugs and includes their creation date and the family name of the creator in the HTTP response:
http://example.com/bugs?oslc.select=dcterms:created,dcterms:creator{foaf:familyName}&oslc.where=cm:severity="high"
Syntax
The
oslc.select
query parameter is defined by the term
oslc_select
in the following BNF grammar:
oslc_select ::= "oslc.select=" properties
The
oslc.select
query parameter uses the same syntax as the
oslc.properties
query parameter. The difference between them is in the meaning of the identifers. In
oslc.properties
, the identifiers are the names of properties of the starting subject resource. In
oslc.select
, the starting subject resource has an associated list of member resources, and the identifers are the names of properties of the resources that are contained in the member list
For example, suppose that a bug resource has the membership property
cm:comment
that relates it to comment resources, and that the bug and each comment have
dcterms:modified
properties that give their last modification dates. The following query specifes that the response should include the modification date of bug 4242 and the modification date of each of its comments:
http://example.com/bugs/4242?oslc.properties=dcterms:modified&oslc.select=dcterms:modified
wildcard
As in the case of
oslc.properties
, the
wildcard
is equivalent to the list of all properties of the member resources. The query parameter
oslc.select=*
specifies that pattern
MUST match all the properties of the resources in the member list.
URL Encoding
The query parameter syntax defined in this specification permits the use of characters that
MUST be properly encoded when transmitted in HTTP requests. For example:
Not encoded:
?oslc.where=dcterms:title="test case 1" and dcterms:modified>="2008-12-02T18:42:30"
Encoded:
?oslc.where=dc%3Atitle%3D%22test%20case%201%22%20and%20dc%3Amodified%3E%3D%222008-12-02T18%3A42%3A30%22
Appendix A: References
These are the specifications referenced by the OSLC Core Query Guidance.