RDFlib OWL TIME Functions

This Python package implements functions to ascertain the temporal relations of objects in RDF graphs.

This package invents SPARQL functions that are based on logic provided in OWL TIME and are named similarly to TIME's Temporal Entity's predicates, for example, the function isBefore() correlates to time:before, i.e. isBefore(a, b) will test to see if time:before should be applied between object a & b.

The functions are made available as functions in RDFlib's SPARQL implementation where they can be called by IRI, e.g. isBefore(a, b) is called tfun:isBefore(?a, ?b). All functions are posed as questions, "is before", and return an RDF literal true or false.

This repository also contains a formal declaration of the functions that this package implements as a SKOS vocabulary. See the Vocabulary section below.

Installation

Normal Python package installation e.g. from PyPI: pip install timefuncs.

This package's only non-standard dependency is RDFlib.

Use

These functions are implemented in RDFlib Python in the file timefuncts/funcs.py and are imported into timefuncs/__init__.py and registered there in RDFlib as SPARQL extension functions with their IRIs.

This means they can be used like this (full working script):

from rdflib import Graph
from timefuncs import TFUN


data = """
    PREFIX : <http://example.com/>
    PREFIX time: <http://www.w3.org/2006/time#>    
    
    :a01 a time:TemporalEntity .    
    :b01 a time:TemporalEntity .
    :c01 a time:TemporalEntity .
    :d01 a time:TemporalEntity .
    
    :a01 time:before :c01 .

    :b01 time:after :c01 .
    """

g = Graph().parse(data=data)

q = """
    PREFIX tfun: <https://w3id.org/timefuncs/>

    SELECT *
    WHERE {
        ?x a time:TemporalEntity .
        ?y a time:TemporalEntity .
        
        FILTER tfun:isBefore(?x, ?y)
    }
    """
for r in g.query(q):
    print(f"{r['x']} is before {r['y']}")

The above stript outputs:

http://example.com/a01 is before http://example.com/b01
http://example.com/a01 is before http://example.com/c01
http://example.com/b01 is before http://example.com/c01

The above script is run using an environment that has had the time functions registered with its copy of rdflib (perhaps by running pip install timefuncs) so that there is no need to import anything other than rdfib and the time functions namespace (from timefuncs import TFUN). It may appear that the namespace is not used but it is, internally! No need to re-declare tfun: as a PREFIX in the SPARQL query...

The time function used here, tfun:isBefore, is called as a filter function to return true when the first given object, here ?x is before the second given object, ?y.

This example uses a pretty open-ended graph pattern match (`?x ?p ?y).

Working with Reasoning / Inferencing

These functions don't assume that any reasoning has been carried out on data and will correctly interpret time:before / time:after and similar inverses, transitive relations (chains of properties) and so on. But there are limits: you will always be able to invent highly complex relations between time:TemporalEntity instances that these functions won't correctly work with.

To work with highly complex data, try reasoning over your data first with OWL TIME's axioms before running these functions. To do this, you need a tool that can calculate OWL "RL" inferences, such as rdflib's OWL-RL. Many triplestores have OWL-RL reasoning capability built-in or as add ons.

Functions

Functions in this package are implemented as SPARQL extension functions with the namespace https://w3id.org/timefuncs/, e.g. isBefore()'s full IRI is https://w3id.org/timefuncs/isBefore.

Python implementations are named the same as the SPARQL functions, but in snake_case, not camelCase, e.g. SPARQL's isBefore() is implemented in Python's is_before().

Functions implemented so far, and their corresponding TIME relations:

These functions are yet to be implemented:

Non-TIME functions

The following proposed functions are inspired by OWL TIME but not directly related to its predicates or classes:

Implementation logic

Functions implemented test for every conceivable way that a temporal relation may be found to be true in given data. For example, isBefore(a, b) will return true if:

• the predicate time:before is given between a & b, or any chain of objects a ... n ... b
• the predicate time:after is given between b & a, or any chain of objects b ... n ... a
• any chain of time:before & time:after links a & b, all pointing in the right directions
• the end of a is declared as being before b or the start of b
  • i.e. for <a> time:hasEnd <a_end> . and <b> time:hasBeginning <b_beginning> ., isBefore(a, b) is true if <a_end> time:before <b_beginning>
• the start of b is declared as being after a or the end of a
• a can be calculated as being before b, based on their instantaneous times or start and end times
  • i.e. for <a> time:inXSDDateTimeStamp <a_xsd> . and <b> time:inXSDDateTimeStamp <b_xsd> . or <a> time:hasEnd/time:inXSDDateTimeStamp <a_xsd> . and <b> time:hasEnd/time:inXSDDateTimeStamp <b_xsd> ., isBefore(a, b) is true if <a_xsd> <b_xsd>

Vocabulary

The time functions, both implemented and to-be implemented, are listed in a SKOS vocabulary, the source files for which are given in the voc/ folder within this repository. The vocabulary is presented online in both RDF (turtle) and HTML (Markdown) formats from these source files, accessible via the namespace IRI:

• https://w3id.org/timefuncs/voc - HTML
• https://w3id.org/timefuncs/voc.ttl - RDF

Each function's IRI resolves to its Concept entry in the vocbaulary, for example, https://w3id.org/timefuncs/isContainedBy --> https://github.com/RDFLib/timefuncs/blob/master/voc/timefuncs.md#is-contained-by.

(The Markdown is auto-generated from the RDF using pyLODE)

Testing

All tests are in tests/ and implemented using pytest.

There are individual tests for each function, e.g. tests/test_is_before.py for isBefore() as well as a test file to rn all tests againts OWL TIME's test suite): tests/test_test_suite.py.

Contributing

Via GitHub, Issues & Pull Requests:

• https://github.com/rdflib/timefuncs

License

This code is licensed with the BSD 3-clause license as per LICENSE which is the same license as used for rdflib.

Citation

@software{https://github.com/rdflib/timefuncs,
  author = {{Nicholas J. Car}},
  title = {RDFlib OWL TIME Functions},
  version = {0.0.2},
  date = {2021},
  url = {https://github.com/rdflib/timefuncs}
}

Contact

Creator & maintainer:
Nicholas J. Car
Data System Architect
SURROUND Australia Pty Ltd
nicholas.car@surroundaustrlaia.com
and
Adjunct Senior Lecturer
College of Engineering & Computer Science
Australian National University
nicholas.car@anu.edu.au

https://orcid.org/0000-0002-8742-7730