This module implements the Swish script processor: it parses a script from a supplied string, and returns a list of Swish state transformer functions whose effect, when applied to a state value, is to implement the supplied script.

The script syntax is based loosely on Notation3, and the script parser is an extension of the Notation3 parser in the module Swish.RDF.Parser.N3. The comment character is # and white space is ignored.

script            := command *
command           := prefixLine        |
                     nameItem          |
                     readGraph         |
                     writeGraph        |
                     mergeGraphs       |
                     compareGraphs     |
                     assertEquiv       |
                     assertMember      |
                     defineRule        |
                     defineRuleset     |
                     defineConstraints |
                     checkProofCmd     |
                     fwdChain          |
                     bwdChain 

prefixLine        := @prefix [<prefix>]: <uri> .

Define a namespace prefix and URI.

The prefix thus defined is available for use in any subsequent script command, and also in any graphs contained within the script file. (So, prefix declarations do not need to be repeated for each graph contained within the script.)

Graphs read from external files must contain their own prefix declarations.

Example:

@prefix gex: <http://example1.com/graphs/>.
@prefix :    <http://example2.com/id/>.

nameItem          := name :- graph     |
                     name :- ( graph* )

Graphs or lists of graphs can be given a name for use in other statements. A name is a qname (prefix:local) or a URI enclosed in angle

Example:

@prefix ex1: <http://example.com/graphs/> .
@prefix ex2: <http://example.com/statements/> .

ex1:gr1 :- { 
    ex2:foo a ex2:Foo .
    ex2:bar a ex2:Bar .
    ex2:Bar rdfs:subClassOf ex2:Foo .
}

readGraph         := @read name [<uri>]

The @read command reads in the contents of the given URI - which at present only supports reading local files, so no HTTP access - and stores it under the given name.

If no URI is given then the file is read from standard input.

Example:

@prefix ex: <http://example.com/> .
@read ex:foo <foo.n3>

writeGraph        := @write name [<uri>] ; comment

The @write command writes out the contents of the given graph - which at present only supports writing local files, so no HTTP access. The comment text is written as a comment line preceeding the graph contents.

If no URI is given then the file is written to the standard output.

Example:

@prefix ex: <http://example.com/> .
@read ex:gr1 <graph1.n3>
@read ex:gr2 <graph2.n3>
@merge (ex:gr1 ex:gr2) => ex:gr3
@write ex:gr3 ; the merged data
@write ex:gr3 <merged.n3> ; merge of graph1.n3 and graph2.n3

mergeGraphs       := @merge ( name* ) => name

Create a new named graph that is the merge two or more graphs, renaming bnodes as required to avoid node-merging.

When the merge command is run, the message

# Merge: <output graph name>

will be created on the standard output channel.

Example:

@prefix gex: <http://example.com/graph/>.
@prefix ex: <http://example.com/statements/>.
gex:gr1 :- { ex:foo ex:bar _:b1 . }
gex:gr2 :- { _:b1 ex:foobar 23. }
@merge (gex:gr1 gex:gr2) => gex:gr3
@write gex:gr3 ; merged graphs

When run in Swish, this creates the following output (along with several other namespace declarations):

# merged graphs
@prefix ex: <http://example.com/statements/> .
ex:foo ex:bar [] .
[
 ex:foobar "23"^^xsd:integer
] .

compareGraphs     := @compare name name

Compare two graphs for isomorphism, setting the Swish exit status to reflect the result.

When the compare command is run, the message

# Compare: <graph1> <graph2>

will be created on the standard output channel.

Example:

@prefix gex: <http://example.com/graphs/>.
@read gex:gr1 <graph1.n3>
@read gex:gr2 <graph2.n3>
@compare gex:gr1 gex:gr2

assertEquiv       := @asserteq name name ; comment

Test two graphs or lists of graphs for isomorphism, reporting if they differ. The comment text is included with any report generated.

When the command is run, the message

# AssertEq: <comment>

will be created on the standard output channel.

Example:

@prefix ex:  <http://id.ninebynine.org/wip/2003/swishtest/> .

# Set up the graphs for the rules
ex:Rule01Ant :- { ?p ex:son ?o . }
ex:Rule01Con :- { ?o a ex:Male ; ex:parent ?p . }

# Create a rule and a ruleset
@rule ex:Rule01 :- ( ex:Rule01Ant ) => ex:Rule01Con
@ruleset ex:rules :- (ex:TomSonDick ex:TomSonHarry) ; (ex:Rule01)

# Apply the rule
@fwdchain ex:rules ex:Rule01 { :Tom ex:son :Charles . } => ex:Rule01fwd

# Compare the results to the expected value
ex:ExpectedRule01fwd :- { :Charles a ex:Male ; ex:parent :Tom . }  
@asserteq ex:Rule01fwd ex:ExpectedRule01fwd
   ; Infer that Charles is male and has parent Tom

assertMember      := @assertin name name ; comment

Test if a graph is isomorphic to a member of a list of graphs, reporting if no match is found. The comment text is included with any report generated.

Example:

@bwdchain pv:rules :PassengerVehicle ex:Test01Inp <= :t1b

@assertin ex:Test01Bwd0 :t1b ; Backward chain component test (0)
@assertin ex:Test01Bwd1 :t1b ; Backward chain component test (1)

defineRule        := @rule name :- ( name* ) => name
defineRule        := @rule name :- ( name* ) => name
                      | ( (name var*)* )

Define a named Horn-style rule.

The list of names preceding and following => are the antecedent and consequent graphs, respectivelu. Both sets may contain variable nodes of the form ?var.

The optional part, after the | separator, is a list of variable binding modifiers, each of which consists of a name and a list of variables (?var) to which the modifier is applied. Variable binding modifiers are built in to Swish, and are used to incorporate datatype value inferences into a rule.

defineRuleset     := @ruleset name :- ( name* ) ; ( name* ) 

Define a named ruleset (a collection of axioms and rules). The first list of names are the axioms that are part of the ruleset, and the second list are the rules.

defineConstraints := @constraints pref :- ( name* ) | [ name | ( name* ) ]

Define a named ruleset containing class-restriction rules based on a datatype value constraint. The first list of names is a list of graphs that together comprise the class-restriction definitions (rule names are the names of the corresponding restriction classes). The second list of names is a list of datatypes whose datatype relations are referenced by the class restriction definitions.

fwdChain          := @fwdchain pref name ( name* ) => name

Define a new graph obtained by forward-chaining a rule. The first name is the ruleset to be used. The second name is the rule name. The list of names are the antecedent graphs to which the rule is applied. The name following the => names a new graph that is the result of formward chaining from the given antecedents using the indicated rule.

bwdChain          := @bwdchain pref name graph <= name

Define a new list of alternative graphs obtained by backward-chaining a rule. The first name is the ruleset to be used. The second name is the rule name. The third name (before the <=) is the name of a goal graph from which to backward chain. The final name (after the <=) names a new list of graphs, each of which is an alternative antecedent from which the given goal can be deduced using the indicated rule.

checkProofCmd     := proofLine nl
                     inputLine nl
                     (stepLine nl)*
                     resultLine
proofLine         := @proof name ( name* )

Check a proof, reporting the step that fails, if any.

The @proof line names the proof and specifies a list rulesets (proof context) used. The remaining lines specify the input expression (@input), proof steps (@step) and the final result (@result) that is demonstrated by the proof.

inputLine         := @input name

In a proof, indicates an input expression upon which the proof is based. Exactly one of these immediately follows the @proof command.

stepLine          := @step name ( name* ) => name

This defines a step of the proof; any number of these immediately follow the @input command.

It indicates the name of the rule applied for this step, a list of antecedent graphs, and a named graph that is deduced by this step. For convenience, the deduced graph may introduce a new named graph using an expression of the form:

name :- { statements }

resultLine        := @result name

This defines the goal of the proof, and completes a proof definition. Exactly one of these immediately follows the @step commands. For convenience, the result statement may introduce a new named graph using an expression of the form:

name :- { statements }

This is the example script taken from http://www.ninebynine.org/Software/swish-0.2.1.html#sec-script-example with the proof step adjusted so that it passes.

# -- Example Swish script --
#
# Comment lines start with a '#'
#
# The script syntax is loosely based on Notation3, but it is a quite 
# different language, except that embedded graphs (enclosed in {...})
# are encoded using Notation3 syntax.
#
# -- Prefix declarations --
#
# As well as being used for all labels defined and used by the script
# itself, these are applied to all graph expressions within the script 
# file, and to graphs created by scripted inferences, 
# but are not applied to any graphs read in from an external source.

@prefix ex:  <http://id.ninebynine.org/wip/2003/swishtest/> .
@prefix pv:  <http://id.ninebynine.org/wip/2003/swishtest/pv/> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
@prefix xsd_integer: <http://id.ninebynine.org/2003/XMLSchema/integer#> .
@prefix rs_rdf:  <http://id.ninebynine.org/2003/Ruleset/rdf#> .
@prefix rs_rdfs: <http://id.ninebynine.org/2003/Ruleset/rdfs#> .
@prefix :   <http://id.ninebynine.org/default/> .

# Additionally, prefix declarations are provided automatically for:
#    @prefix rdf:   <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
#    @prefix rdfs:  <file://www.w3.org/2000/01/rdf-schema#> .
#    @prefix rdfd:  <http://id.ninebynine.org/2003/rdfext/rdfd#> .
#    @prefix rdfo:  <http://id.ninebynine.org/2003/rdfext/rdfo#> .
#    @prefix owl:   <http://www.w3.org/2002/07/owl#> .

# -- Simple named graph declarations --

ex:Rule01Ant :- { ?p ex:son ?o . }

ex:Rule01Con :- { ?o a ex:Male ; ex:parent ?p . }

ex:TomSonDick :- { :Tom ex:son :Dick . }
ex:TomSonHarry :- { :Tom ex:son :Harry . }

# -- Named rule definition --

@rule ex:Rule01 :- ( ex:Rule01Ant ) => ex:Rule01Con

# -- Named ruleset definition --
#
# A 'ruleset' is a collection of axioms and rules.
#
# Currently, the ruleset is identified using the namespace alone;
# i.e. the 'rules' in 'ex:rules' below is not used.  
# This is under review.

@ruleset ex:rules :- (ex:TomSonDick ex:TomSonHarry) ; (ex:Rule01)

# -- Forward application of rule --
#
# The rule is identified here by ruleset and a name within the ruleset.

@fwdchain ex:rules ex:Rule01 { :Tom ex:son :Charles . } => ex:Rule01fwd

# -- Compare graphs --
#
# Compare result of inference with expected result.
# This is a graph isomorphism test rather than strict equality, 
# to allow for bnode renaming.
# If the graphs are not equal, a message is generated, which
# includes the comment (';' to end of line)

ex:ExpectedRule01fwd :- { :Charles a ex:Male ; ex:parent :Tom . }  

@asserteq ex:Rule01fwd ex:ExpectedRule01fwd
   ; Infer that Charles is male and has parent Tom

# -- Display graph (to screen and a file) --
#
# The comment is included in the output.

@write ex:Rule01fwd ; Charles is male and has parent Tom
@write ex:Rule01fwd <Example1.n3> ; Charles is male and has parent Tom

# -- Read graph from file --
#
# Creates a new named graph in the Swish environment.

@read ex:Rule01inp <Example1.n3>

# -- Proof check --
#
# This proof uses the built-in RDF and RDFS rulesets, 
# which are the RDF- and RDFS- entailment rules described in the RDF
# formal semantics document.
#
# To prove:
#     ex:foo ex:prop "a" .
# RDFS-entails
#     ex:foo ex:prop _:x .
#     _:x rdf:type rdfs:Resource .
#
# If the proof is not valid according to the axioms and rules of the 
# ruleset(s) used and antecedents given, then an error is reported 
# indicating the failed proof step.

ex:Input  :- { ex:foo ex:prop "a" . }
ex:Result :- { ex:foo ex:prop _:a . _:a rdf:type rdfs:Resource . }

@proof ex:Proof ( rs_rdf:rules rs_rdfs:rules )
  @input  ex:Input
  @step   rs_rdfs:r3 ( rs_rdfs:a10 rs_rdfs:a39 )
          => ex:Stepa :- { rdfs:Literal rdf:type rdfs:Class . }
  @step   rs_rdfs:r8 ( ex:Stepa )
          => ex:Stepb :- { rdfs:Literal rdfs:subClassOf rdfs:Resource . }
  @step   rs_rdf:lg ( ex:Input )
          => ex:Stepc :- { ex:foo ex:prop _:a . _:a rdf:_allocatedTo "a" . }
  @step   rs_rdfs:r1 ( ex:Stepc )
          => ex:Stepd :- { _:a rdf:type rdfs:Literal . }
  @step   rs_rdfs:r9 ( ex:Stepb ex:Stepd )
          => ex:Stepe :- { _:a rdf:type rdfs:Resource . }
  @step   rs_rdf:se  ( ex:Stepc ex:Stepd ex:Stepe )
          => ex:Result
  @result ex:Result

# -- Restriction based datatype inferencing --
#
# Datatype inferencing based on a general class restriction and
# a predefined relation (per idea noted by Pan and Horrocks).

ex:VehicleRule :-
  { :PassengerVehicle a rdfd:GeneralRestriction ;
      rdfd:onProperties (:totalCapacity :seatedCapacity :standingCapacity) ;
      rdfd:constraint xsd_integer:sum ;
      rdfd:maxCardinality "1"^^xsd:nonNegativeInteger . }

# Define a new ruleset based on a declaration of a constraint class
# and reference to built-in datatype.
# The datatype constraint xsd_integer:sum is part of the definition 
# of datatype xsd:integer that is cited in the constraint ruleset
# declaration.  It relates named properties of a class instance.

@constraints pv:rules :- ( ex:VehicleRule ) | xsd:integer

# Input data for test cases:

ex:Test01Inp :-
  { _:a1 a :PassengerVehicle ;
      :seatedCapacity "30"^^xsd:integer ;
      :standingCapacity "20"^^xsd:integer . }

# Forward chaining test case:

ex:Test01Fwd :- { _:a1 :totalCapacity "50"^^xsd:integer . }

@fwdchain pv:rules :PassengerVehicle ex:Test01Inp => :t1f
@asserteq :t1f ex:Test01Fwd  ; Forward chain test

# Backward chaining test case:
#
# Note that the result of backward chaining is a list of alternatives,
# any one of which is sufficient to derive the given conclusion.

ex:Test01Bwd0 :-
  { _:a1 a :PassengerVehicle .
    _:a1 :totalCapacity "50"^^xsd:integer .
    _:a1 :seatedCapacity "30"^^xsd:integer . }

ex:Test01Bwd1 :-
  { _:a1 a :PassengerVehicle .
    _:a1 :totalCapacity "50"^^xsd:integer .
    _:a1 :standingCapacity "20"^^xsd:integer . }

# Declare list of graphs:

ex:Test01Bwd :- ( ex:Test01Bwd0 ex:Test01Bwd1 )

@bwdchain pv:rules :PassengerVehicle ex:Test01Inp <= :t1b
@asserteq :t1b ex:Test01Bwd  ; Backward chain test

# Can test for graph membership in a list

@assertin ex:Test01Bwd0 :t1b ; Backward chain component test (0)
@assertin ex:Test01Bwd1 :t1b ; Backward chain component test (1)

# -- Merge graphs --
#
# Merging renames bnodes to avoid collisions.

@merge ( ex:Test01Bwd0 ex:Test01Bwd1 ) => ex:Merged

# This form of comparison sets the Swish exit status based on the result.

ex:ExpectedMerged :-
  { _:a1 a :PassengerVehicle .
    _:a1 :totalCapacity "50"^^xsd:integer .
    _:a1 :seatedCapacity "30"^^xsd:integer .
    _:a2 a :PassengerVehicle .
    _:a2 :totalCapacity "50"^^xsd:integer .
    _:a2 :standingCapacity "20"^^xsd:integer . }

@compare ex:Merged ex:ExpectedMerged

# End of example script

If saved in the file example.ss, then it can be evaluated by saying either of:

% Swish -s=example.ss

or, from ghci:

Prelude> :set prompt "Swish> "
Swish> :m + Swish
Swish> runSwish "-s=example.ss"

and the output is

# AssertEq: Infer that Charles is male and has parent Tom
# Charles is male and has parent Tom
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix rdfd: <http://id.ninebynine.org/2003/rdfext/rdfd#> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .
@prefix log: <http://www.w3.org/2000/10/swap/log#> .
@prefix : <http://id.ninebynine.org/default/> .
@prefix ex: <http://id.ninebynine.org/wip/2003/swishtest/> .
@prefix pv: <http://id.ninebynine.org/wip/2003/swishtest/pv/> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
@prefix xsd_integer: <http://id.ninebynine.org/2003/XMLSchema/integer#> .
@prefix rs_rdf: <http://id.ninebynine.org/2003/Ruleset/rdf#> .
@prefix rs_rdfs: <http://id.ninebynine.org/2003/Ruleset/rdfs#> .
:Charles ex:parent :Tom ;
         a ex:Male .

Proof satisfied: ex:Proof
# AssertEq: Forward chain test
# AssertEq: Backward chain test
# AssertIn: Backward chain component test (0)
# AssertIn: Backward chain component test (1)
# Merge: ex:Merged
# Compare: ex:Merged ex:ExpectedMerged