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

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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

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(’2002-01-01’,’2004-12-31’)’) 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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

? 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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

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 2008 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 [1992-04-01, UC) Version N: valid [1992-04-01,2008-01-01) Version N+1: valid [2008-01-01, UC) SEMAPRO 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

“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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

“The Valid Ontology” Encoding (1) ... <version num=“30"> <timeStamp from="1992-04-01" to=“9999-99-99" /> <owl:Class rdf:ID="Retired"> <rdfs:subClassOf rdf:resource="#Citizen" /> </owl:Class> <version num=“31"> <timeStamp from="2008-01-01" to="9999-99-99" /> <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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

“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="1992-04-01" to=“9999-99-99" /> <owl:Class rdf:ID="Retired"> <rdfs:subClassOf rdf:resource="#Citizen" /> </owl:Class> <version num=“31"> <timeStamp from="2008-01-01" to="9999-99-99" /> <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 2008-06-01 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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

The “Valid Ontology” Encoding (3) ... <owl:Class rdf:ID="Retired"> <rdfs:subClassOf rdf:resource="#Citizen" /> </owl:Class> ... <version num=“30"> <timeStamp from="1992-04-01" to=“9999-99-99" /> <owl:Class rdf:ID="Retired"> <rdfs:subClassOf rdf:resource="#Citizen" /> </owl:Class> <version num=“31"> <timeStamp from="2008-01-01" to="9999-99-99" /> <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 2007-06-01 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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework

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 2009 - Grandi, Scalas – The Valid Ontology: a Simple OWL Temporal Versioning Framework