1. The Valid Ontology: a simple OWL Temporal Versioning Framework
Third International Conference on Advances in Semantic Processing - SEMAPRO 2009
The Valid Ontology: a simple OWL Temporal Versioning Framework
Fabio Grandi, Maria Rita Scalas
Alma Mater Studiorum - Università degli Studi di Bologna

2. Overview
Our research activities concern the implementation of Web information systems for e-Government applications
Development of e-Government initiatives: more and more on-line documents and services are being made available by Public Administrations
We make use of temporal database and semantic Web techniques to provide personalized access to such resources
In particular, we consider multi-version resources (norm documents and service specifications) stored in Web repositories in XML format
This work is part of a reasearch activity concerning eGov applications. In recent years, there has been a great development of eGov initiatives pushed by PAs with more and more resources made available on the web. We use TDB and SW techniques to support personalized access and, as resources, we consider multi-version norm documents (laws, decrees, regulations etc) and service specifications in XML format.
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

3. A Personalization Framework for e-Government Applications
XML
Personalized Resource
Personalization Engine
User Query
Citizen
Digital identity
Self-employed
User Profile
The personalization framework we consider is composed of a multi-version resource repository which is accessed through a personalization engine. The citizen using the system can express queries and, in the meantime, by means of his digital identity, is classified wrt an ontology. The results of the classification is used as user profile by the personalization engine and together with the user query allows the engine to retrieve and reconstruct a personalized version of the desired resource.
XML
Multi-version Resource Repository
Civic Ontology
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

4. Importance of versioning
Temporal concerns are ubiquitous in the legal domain:
A norm text changes in time due to subsequent modifications, evolving through a sequence of temporal versions
The ability to capture temporal versioning is essential for the management of norm documents in a dynamic environment
it is crucial to reconstruct the consolidated version of a norm
also past versions are still important! 2
new version
Original norm text 3
new version 1
time
In this context, temporal aspects are very important, and widespread in the legal domain. As a matter of fact, norms are subject to amendments and changes and, thus, starting from an initial text, modifying norms produce a sequence of versions, the most important of which is the last one, the so-called consolidated version (which takes into account all the effected modifications), but also past versions are still important and are often searched by queries.
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

5. Importance of versioning
Applicability (semantic) versioning also plays an important role
some norms or some of their parts have or acquire a limited applicability
personalized version of the norm:
A version only containing provisions which are applicable to a citizen’s personal case
Self-employed
Another important versioning dimension is semantic and involves the applicability of a norm or of a norm portion to a limited set of citizens. Hence we can define the personalized version of a norm as the one composed of the provisions which are all applicable to a citizen or to a homogeneous class of citizens.
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

6. Semantic versioning
Aimed at providing personalized access to resources (documents and services) with respect to applicability
Civic ontology: a classification of citizens based on the distinctions introduced by successive norms (founding acts) that imply some limitations in their applicability
In order to support personalized access wrt applicability, we introduced an ontology called civic ontology, which captures a classification of citizens wrt to the distinctions introduced by norms (which we call the founding acts of the civic ontology) with limitations in their applicability. In this example we can see a civic ontology built using as founding acts a corpus of laws concerning tax treatment.
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

7. Semantic versioning
At this stage of the project, we manage “tree-like” ontologies
class taxonomies induced by the IS-A relationship
we exploit the pre-order and post-order properties of trees
Applicability of different parts of a norm text to the relevant classes of the civic ontology is used as a new versioning dimension
In this project we consider tree-shaped ontologies, that is taxonomies induced by the ISA relationship and for which codes corresponding to the pre-order and post-order visit of the tree can be assigned to nodes. Pre-order codes are also used as class identifiers. Reference to node Ids can then be added to resources as XML annotations to define versions with different applicability.
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

8. Semantic versioning
Applicability is inherited by descendant nodes unless locally redefined
By means of redefinitions we can also introduce, for each part of a document, complex applicability properties
Extensions with respect to ancestors
Restrictions with respect to ancestors
In the XML structure of resources, applicability is inherited by descendant nodes unless locally extended or restricted.
For example, art.1 is applicable to class 3, that is employees, an to all its subclasses. Its first paragraph is applicable to class 4, which is a restriction, whereas its second paragraph is applicable to class 3 by inheritance but also to class 8 by redefinition, which is an extension.
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

9. The Personalization Engine
Based on a Temporal Multi-version XML Query Processor:
provides all the structural, textual, temporal, and applicability query
facilities in a single component
exploits ad-hoc data structures and
algorithms to obtain high efficiency
allows users to retrieve and
reconstruct on-the-fly XML document versions satisfying the four types of constraints
The personalization engine is a powerful multi-version XML query processor implemented in Java, which is able to execute flexible user queries involving structural, textual, temporal and applicability constraints. In order to obtain a high query efficiency, XML resources are stored in a partitioned way and the engine exploits ad-hoc structural join algorithms. Resources satisfying the query constraints are retrieved and assembled on-the-fly to produce the desired personalized versions.
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

10. Example of full search John Smith is a self-employed citizen.
He is interested in the text of all the norms ...
... which contain paragraphs dealing with health care, ...
... which were valid between 2002 and 2004, ...
... and which are applicable to his case (civic class 7).
Structural constraint
Textual constraint
Temporal constraint
Applicability constraint
As an example of query that can be executed, we assume a citizen J.S. using the system and who is classified as belonging to the self-employed ontology class. He is interested in…
4 orthogonal constraints
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

11. Example of full search Structural constraint Textual constraint
FOR $a IN norms
WHERE textConstr ($a//paragraph//text(), ’health AND care’)
AND tempConstr (’vTime OVERLAPS PERIOD(’ ’,’ ’)’)
AND applConstr (’class 7’)
RETURN $a
Structural constraint
Textual constraint
Temporal constraint
Applicability constraint
Such constraints can all be expressed in a XQuery-like statement that can be executed by the multi-version XML processor.
4 orthogonal constraints
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

12. ? What’s new? There is a missing tile in the puzzle:
Maintenance of temporal versions of the civic ontology is also required ?
So far, I presented the framework as it was before this work. Actually, we did not consider an important feature: also the ontology used for classification needs temporal versioning.
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

13. Ontology Versioning
As also founding acts are subject to modifications, also the civic ontology evolves through subsequent temporal versions
For instance, a new law effective from 2008 allows retired persons to work again as self-employed. A new ontology version valid from with a new class “Self-employed Retired” is then created.
New founding act
In particular, also the ontology evolves through successive versions as produced by subsequent founding acts. For example, the ontology we saw in previous slides is actually its N-th version valid form April 1992 on (UC means Until Changed). It needs modifications, if a new founding act effective from 2008 states that Retired persons can work again as self-employed while retaining their pension. Then a new ontology version valid from 2008 is created with a new intersection class “self-employed retired”
new version
Self-employed Retired
Version N: valid [ , UC)
Version N: valid [ , )
Version N+1: valid [ , UC)
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

14. Consistent temporal perspective
When searching for a past version of a resource, the same temporal perspective must be adopted:
for the ontology version used for user classification
for the resource version to be retrieved by the personalization engine
Example:
one Court has to pass judgment today on a crime committed by a citizen in the past (e.g. in 2007)
in order to consider the correct legal framework, the laws of interest are those which where applicable in 2007 to that crime
in order to find out the right personalized version of these laws, the citizen must be classified with respect to the ontology which was also valid in 2007
Temporal versioning of the ontology is necessary to enforce a consistent temporal perspective between the classification of the citizen and for the retrieval of a resource version. For example, in order to find out the laws that must be applied to an accused person for a crime committed in 2007, the laws that were applicable to that crime in 2007 must be retrieved and personalized according to the classification of the accused person wrt the ontology version also valid in 2007.
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

15. Objectives of this work
Completion of the personalization framework:
Multi-version resources are represented in compact format as XML documents
dynamics of resources in time is captured
limited applicability of resources is captured via references to a civic ontology
selective access and reconstruction of versions is supported by an efficient personalization engine
dynamics of the civic ontology in time is captured
Aimed at:
enabling users to access personalized versions of multi-version resources
implementing a consistent temporal perspective for personalization of past resource versions through temporal versioning of the reference ontology
Hence, the objective of the present work is the completion of the personalization framework with the management of a multi-version civic ontology, in order to support a consistent temporal perspective between citizen classification and resource retrieval.
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

16. “The Valid Ontology” Approach
Reuse of the temporal XML Model and Query Engine
A similar temporal multi-version format is used both for documents and for the ontology definition (with timestamps and ah-hoc annotations to define versions)
The same high-efficiency personalization engine used for documents is also used for extracting ontology versions
Encoding of a Multi-version OWL Ontology in a temporal XML document
Ontology versions are OWL documents serialized as RDF/XML
Compact representation of multiple ontology versions into a single XML file
Approach based on standard XML technologies (inspired by “The Valid Web” [Grandi & Mandreoli 2000])
To this purpose, we propose a solution similar to “The valid web” introduced by myself and Mandreoli in 2000 for the temporal management of generic web resources (like html pages). In particular, we propose to use for the multi-version ontologies an encoding scheme similar to the one used for norm documents. Moreover, also the personalization engine can be used to extract single ontology versions form the multi-version store.
We consider ontologies written in OWL (which is a requirements of the eGov application), which will be extended with ad-hoc XML annotations in order to encode multiple versions. This leads to a space-saving representation and relies on standard XML technologies.
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

17. The Personalization Engine
Based on a Temporal Multi-version XML Query Processor:
provides all the temporal, structural,
textual and applicability query
facilities in a single component
exploits ad-hoc data structures and
algorithms to obtain high efficiency
allows users to store and
reconstruct on-the-fly XML document versions satisfying the four types of constraints
can also be used to extract valid OWL ontology versions from a multi-version XML store
Hence, the existing personalization engine can be conveniently used also for ontology version extraction.
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

18. “The Valid Ontology” Encoding (1)
...
<version num=“30">
<timeStamp from=" " to=“ " />
<owl:Class rdf:ID="Retired">
<rdfs:subClassOf rdf:resource="#Citizen" />
</owl:Class>
<version num=“31">
<timeStamp from=" " to=" " />
<owl:Class rdf:ID="SelfEmployedRetired">
<rdfs:subClassOf rdf:resource="#SelfEmployed" />
<rdfs:subClassOf rdf:resource="#Retired" />
</version>
Ontology versions are encoded into an XML file including
<version> elements to delimit version boundaries and
<timeStamp> elements to assign validity to versions
The resulting XML file is not a valid OWL ontology definition because of the new tags
Here is an example of the XML annotations used for the encoding of a multi-version ontology into a single XML file. In addition to OWL code representing the definition of the ontology versions, “version” elements are introduced to mark the boundaries of a version and “timestamp” elements are added to assign the temporal validity to versions. Obviously, the resulting XML file is not a valid OWL ontology definition because of the new tags.
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

19. “The Valid Ontology” Encoding (2)
...
<owl:Class rdf:ID="Retired">
<rdfs:subClassOf rdf:resource="#Citizen" />
</owl:Class>
<owl:Class rdf:ID="SelfEmployedRetired">
<rdfs:subClassOf rdf:resource="#SelfEmployed" />
<rdfs:subClassOf rdf:resource="#Retired" />
...
<version num=“30">
<timeStamp from=" " to=“ " />
<owl:Class rdf:ID="Retired">
<rdfs:subClassOf rdf:resource="#Citizen" />
</owl:Class>
<version num=“31">
<timeStamp from=" " to=" " />
<owl:Class rdf:ID="SelfEmployedRetired">
<rdfs:subClassOf rdf:resource="#SelfEmployed" />
<rdfs:subClassOf rdf:resource="#Retired" />
</version>
Preprocessing with the Temporal XML Query Engine effects a time-slice operation and returns a valid OWL ontology definition
For instance, retrieving the version valid at produces the results shown on the left (a valid OWL file)
However, after preprocessing by the personalization engine which extracts a timeslice, the resulting version is a regular OWL ontology definition. For instance, we can see the version valid at the beginning of June 2008, including the definitions for both classes Retired and SelfEmployed-Retired…
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

20. The “Valid Ontology” Encoding (3)
...
<owl:Class rdf:ID="Retired">
<rdfs:subClassOf rdf:resource="#Citizen" />
</owl:Class>
...
<version num=“30">
<timeStamp from=" " to=“ " />
<owl:Class rdf:ID="Retired">
<rdfs:subClassOf rdf:resource="#Citizen" />
</owl:Class>
<version num=“31">
<timeStamp from=" " to=" " />
<owl:Class rdf:ID="SelfEmployedRetired">
<rdfs:subClassOf rdf:resource="#SelfEmployed" />
<rdfs:subClassOf rdf:resource="#Retired" />
</version>
Preprocessing with the Temporal XML Query Engine effects a time-slice operation and returns a valid OWL ontology definition
For instance, retrieving the version valid at produces the results shown on the left (a valid OWL file)
… and the version valid at the beginning of June 2007, which only includes the definition of class Retired.
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

21. Conclusions
We presented our research work concerning the design and implementation of Web-based information systems for e-Government applications supporting ontology-based personalized access to multi-version resources in XML format
We introduced “The Valid Ontology” approach, a simple framework based on standard XML technology to manage temporal versions of OWL ontologies
Multi-version ontologies are encoded in a compact form into a single XML file
XML tags are added to OWL documents to mark the boundaries of versioned portions and to assign timestamps to versions
An XML Query Processor is used to extract single ontology versions as temporal snapshots
In particular, the very efficient Temporal XML Query Processor used as personalization engine can also be used to this purpose
In conclusion…
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

22. Future Work
Assessment of “The Valid Ontology” approach in a real e-Government scenario
with ontology versions built according to the founding acts belonging to a corpus of real norms
Extension of the personalization framework to other application fields with similar requirements (e.g. management of Clinical Guidelines)
Study of the management of temporal versions of ontologies adopting different encoding formats
Management of temporal RDF with triple store technologies
Addition of version timestamps through the annotation feature proposed for the OWL 2 language
In our future work, we plan to assess “The Valid Ontology” approach in a real eGov scenario, building the multi-version ontology according to a real corpus of founding acts.
Moreover, we plan to extend our framework to other application fields with similar personalization requirements, like the management of clinical guidelines in the medical domain.
Finally, we also plan to consider alternative ways to manage temporal multi-version ontologies, also considering other encoding formats, like RDF and OWL 2.
SEMAPRO Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework