tolog 1.0

2.1 The clause list

The clause list is the main part of the query, and is defined as follows.

Clause lists

A clause list consists of individual clauses.

Clauses

Clauses come in four kinds, each of which is defined below.

Predicate clauses

Operator clauses

Or clauses

Not clauses

Language particles

Note how double quotes inside strings are escaped by repeating them; two double quotes parse into a single double quote.

Ed. Note:
URI resolution. Scope rules. Duplicate rules. Identifier presedence rules.

2.2 The head

Ed. Note:
Allow rule defs here.

Heads

2.3 The tail

The tail is defined as follows.

Tails

2.4 Rule files

Tolog predicates may be defined in rule files, which have the syntax defined below. How these rule files are made available to the processor is not defined in this version of tolog.

Rule sets

3.1 Evaluating references

References can be evaluated in two ways: as references to TMDM information items or as references to predicates.

3.2 Clauselist evaluation

The clauselist is evaluated by processing each clause in order. The input to the first clause is a query result consisting of a single empty variable binding set. All the following clauses receive the query result produced by the previous clause as input, and the result of the entire clauselist is that produced by the last clause.

5.1 Generative predicates

A number of the built-in predicates are defined in terms of a rule that generates all possible values that make the predicate true.

Ed. Note:
Add text explaining how to evaluate this.

5.2 association

The predicate association($ASSOC) generates the matches produced by traversing the set of association items in the [associations] property of the topic map item and binding $ASSOC to each one in turn.

5.3 association-role

The predicate association-role($ASSOC, $ROLE) generates the matches produced by traversing the set of association items in the [associations] property of the topic map item and then for each association role item in the [roles] property of each association item producing a match where $ASSOC is bound to the association item, and $ROLE to the association role item.

5.4 base-locator

The predicate base-locator($LOC) generates no matches if the [base locator] property of the topic map item is null. If it is not a single match is produced where $LOC is bound to the locator item in that property.

5.5 occurrence

The predicate occurrence($TOPIC, $OCC) generates the matches produced by traversing the set of topic items in the [topics] property of the topic map item and then for each occurrence item in the [occurrences] property of each topic item producing a match where $TOPIC is bound to the topic item, and $OCC to the occurrence item.

5.6 reifies

The predicate reifies($REIFIER, $REIFIED) generates the matches produced by traversing the set of topic items in the [topics] property of the topic map item and then for each information item in the [reified] property of each topic item producing a match where $REIFIER is bound to the topic item, and $REIFIED to the information item.

5.7 resource

5.8 role-player

5.9 scope

5.10 source-locator

5.11 subject-identifier

5.12 subject-locator

5.13 topic

5.14 topic-name

5.15 topicmap

5.16 type

5.17 value

5.18 variant

5.19 direct-instance-of

The direct-instance-of predicate can be defined using the following rule.

direct-instance-of($INSTANCE, $CLASS) :-
  i"http://psi.topicmaps.org/sam/1.0/#type-instance"(
    $INSTANCE : i"http://psi.topicmaps.org/sam/1.0/#instance",
    $CLASS    : i"http://psi.topicmaps.org/sam/1.0/#class").

In implementations where the type-instance relationship is represented directly implementations must evaluate this as if the relationship were always represented using associations.

5.20 instance-of

The instance-of predicate can be defined in terms of the direct-instance-of predicate using the following rules file.

instance-of($INSTANCE, $CLASS) :- {
  direct-instance-of($INSTANCE, $CLASS) |
  direct-instance-of($INSTANCE, $DCLASS), descendant-of($DCLASS, $CLASS)
}.

descendant-of($DESC, $ANC) :- {
  super-sub($DESC, $ANC) |
  super-sub($DESC, $INT), descendant-of($INT, $ANC)
}.

super-sub($SUB, $SUPER) :-
  i"http://www.topicmaps.org/xtm/1.0/core.xtm#superclass-subclass"(
    $SUB   : i"http://www.topicmaps.org/xtm/1.0/core.xtm#subclass",
    $SUPER : i"http://www.topicmaps.org/xtm/1.0/core.xtm#superclass").

Of course, the descendant-of and super-sub predicates are not visible to tolog queries; they are just included in order to make it possible to define the instance-of predicate.

5.21 value-like