Conformance

As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.

The keywords MAY, MUST, MUST NOT, RECOMMENDED, SHOULD, and SHOULD NOT in this document are to be interpreted as described in BCP 14 RFC2119 RFC8174 when, and only when, they appear in all capitals, as shown here.

A conforming DATALOG-TEXT resource is a Unicode string that MUST conform to the grammar and additional constraints defined in § Datalog Text Grammar, starting with the program production.

A conforming DATALOG-TEXT parser MUST ensure the resource it is provided is a conforming DATALOG-TEXT resource, signalling error conditions specified herein. Additionally, a conforming resolver MUST be able to convert paths to URIs RFC3986 and retrieve the identified resource on behalf of the parser.

Strict vs Lax Processing

Two modes of operation for a conforming DATALOG-TEXT processor are described, a strict processing mode that, while more verbose, relies less on inference of a program’s semantics. For example, when strict processing is enabled all relations both extensional and intensional MUST BE declared by processing instructions. A lax processing mode allows more flexibility in the source and is especially useful in dealing with Datalog written in different dialects.

Strict processing support is RECOMMENDED, and may be enabled by the strict pragma. Where behavior is required by strict processing it will be highlighted in the text. This specification does not define whether a conforming DATALOG-TEXT processor is required to be strict by default.

Media Type and Content Encoding

The media type of DATALOG-TEXT resource is application/vnd.datalog. The content encoding of a DATALOG-TEXT document is always UTF-8. For complete details, see appendix § IANA Considerations.

features Parameter

This parameter is used to indicate the language features the resource requires. The list of supported feature identifiers is in § Language Features.

The content of this parameter is a comma separated list of feature identifiers. This is used as a hint to a conforming DATALOG-TEXT processor to determine if they can process the resource.

While it is clearly of benefit for the set of features listed in this parameter to be exactly the same as the set of language pragmas used in the document it is impossible to guarantee. Therefore, processors MAY choose to proceed parsing the resource or signal an error if they find that these feature lists do not match.

Errors

• ERR_UNSUPPORTED_FEATURE – a feature identifier was not recognized, or supported, by the processor, even if it may be valid in some other version of this specification.

Example

The media type application/vnd.datalog;features=negation,constraints denotes a document with the following feature pragmas.

.pragma negation.
.pragma constraints.

dialect Parameter

This parameter is used to indicate the language dialect the resource conforms to. The list of supported dialect identifiers is in § Dialect Identifiers.

The content of this parameter is a single dialect identifier.

Errors

• ERR_UNSUPPORTED_DIALECT – a dialog identifier was not recognized, or supported, by the processor, even if it may be valid in some other version of this specification.

Language Features

As mentioned in the introduction the language described by DATALOG-TEXT with no additional language features enabled is $\small\text{Datalog}^{\Gamma}$, the language $\small\text{Datalog}$ with typed relation attributes. All the language features defined in this specification MUST BE supported by a conforming DATALOG-TEXT processor. These features are: arithmetic_literals, constraints, disjunction, extended_numerics, functional_dependencies, and negation.

This specification DOES NOT cover the behavior of a DATALOG-TEXT evaluator and so support of these language features only ensures that a DATALOG-TEXT resource can be parsed and validated, not that it can be evaluated. In the case that an evaluator detects a language feature it cannot support it MUST signal the error ERR_UNSUPPORTED_FEATURE.

Dialect Identifiers

The purpose of this parameter is to allow for the identification of Datalog representations that are produced by applications that are not DATALOG-TEXT conformant. These applications may use an alternate syntax for grammar specified by DATALOG-TEXT, or they may extend the language with non-standard features.

MITRE Datalog

This dialect only allows ASCII, Prolog style, operators; :- for material implication, , for conjunction, and ! for negation. The dialect does not support the features constraints, disjunction, or extended_numerics.

The use of other syntaxed defined in this specification MUST signal the error ERR_UNSUPPORTED_SYNTAX.

Example

Note that the absence of the dialect parameter on the MIME type is the same as using the value core. The following values are therefore equivalent.

application/vnd.datalog
application/vnd.datalog;dialect=core