1. A Temporal Data Model and Management System for Normative Texts in XML Format
Fabio Grandi
DEIS - Univ. of Bologna, Italy
Federica Mandreoli, Paolo Tiberio and Marco Bergonzini
DII – Univ. of Modena e Reggio Emilia, Italy

2. Dynamics of norms in time
Temporal concerns are ubiquitous in the law domain
The ability to model temporal dimensions is essential for the management of evolving norms
Temporal database systems
Database systems including special support for the time dimension(s)
Temporal dimensions: valid time, transaction time, event/decision time and availability time (for advanced applications)
There is a much current interest in representing and querying (temporal) XML data

3. Objectives Development of an effective and efficient system where:
dynamics of norms in time is captured
norms are represented as XML documents and are available on the Web
Approach
Definition of a temporal XML model including
A temporal XML schema
Temporal manipulation operations
Design, implementation and evaluation of a system prototype supporting the model

4. The temporal XML data model
Based on the hierarchical organization of normative texts
contents-section-article-paragraph
At each level of the hierarchy, the history of changes is represented by the versions produced
The temporal pertinence is represented by timestamps, i.e. temporal elements encoded as multiple 3-dim intervals (TA)
A reference to the modifying (active) norm is added (an_ref)
Supports ancestor-descendant inheritance
Timestamps of a node are inherited by its descendants
Along the hierarchy, redefinitions can only involve a restriction of the temporal pertinence

5. The temporal XML schema
Law
Num – R
Type – R
Publication – R
Vt_Start – R
Vt_End – O
Tt_Start – R
Tt_End – O
Et_Start – R
Et_End – O
Publication time
time of publication on the Official Journal
Validity time
time the norm is in force
Efficacy time
time the norm can be applied
Transaction time
time the norm is stored in the system
Title
Contents
Vt_Start – R
Vt_End – O
Tt_Start – R
Tt_End – O
Et_Start – R
Et_End – O
An_ref – O
Ver TA
Num – R
Section
Num – R
Vt_Start – R
Vt_End – O
Tt_Start – R
Tt_End – O
Et_Start – R
Et_End – O
An_ref – O
Ver TA
Num – R
Num – R
Heading
Article
Vt_Start – R
Vt_End – O
Tt_Start – R
Tt_End – O
Et_Start – R
Et_End – O
An_ref – O
Ver TA
Num – R
Heading
Paragraph
Num – R
Vt_Start – R
Vt_End – O
Tt_Start – R
Tt_End – O
Et_Start – R
Et_End – O
An_ref – O
Ver TA
Num – R

6. An example document <norm num="2624/1999" type="Law">
<title>Cereals Importation</title>
<contents publication=" " vt_start=" " tt_start=" " et_start=" " > …
<article num="1">
<ver num="1"> <ta/ vt_start=" " tt_start=" " tt_end=" "
et_start=" " >
<ta/ vt_start=" " et_start=" " et_end=" " … > <ta/ vt_start=" " vt_end=" " et_start=" " … >
<paragraph num="1"><ver num="1" > …Art. 1 before modification… </ver>
</paragraph> …
</ver>
<ver num="2" an_ref="LD135/2000" > <ta/ vt_start=" " tt_start=" " et_start=" " >
<paragraph num="1"><ver num="1"> …Art. 1 after modification… </ver> </paragraph>
<paragraph num ="2"><ver num="1"> …Art. 1 after modification… </ver>
</paragraph>
</article>

7. Querying aspects
FOR $a IN path WHERE constraints on $a RETURN const-tree(document($a), temporal specs)
constraints can contain keyword-based text selections
e.g. contains(//title, ‘cereal’)
const-tree
Is an operator for the reconstruction of a temporally consistent normative act (involves temporal selections)
temporal specs may require a temporal predicate for each of the supported dimensions
Defaults:
efficacy time = valid time
T_DIM CONTAINS now
At each level, the text making up the desired version is selected

8. Example of reconstruction (curr. ver.)
<norm num="2624/1999" type="Law">
<title>Cereals Importation</title>
<contents publication=" " vt_start=" " tt_start=" " et_start=" " > …
<article num="1">
<ver num="1"> <ta/ vt_start=" " tt_start=" " tt_end=" "
et_start=" " > <ta/ … > <ta/ … >
<paragraph num="1"><ver num="1" > …Art. 1 before modification… </ver>
</paragraph> …
</ver>
<ver num="2" an_ref="LD135/2000" > <ta/ vt_start=" " tt_start=" " et_start=" " >
<paragraph num="1"><ver num="1"> …Art. 1 after modification… <ver> </paragraph>
<paragraph num ="2"><ver num="1"> …Art. 1 after modification… </ver>
</paragraph>
</article>
( NOT INCLUDED )

9. changeText operation Performs a lossless update of documents Requires
The path of the element to be substituted
The validity and efficacy timestamps to be assigned to the new version
The new text (empty if abrogation)
Steps
Adds a new version
Updates timestamps of the sibling versions
Updates timestamps of ancestor and descendant versions (if necessary)

10. changeTime operation
Modifies the timestamps of an existing document portion
Requires
The path of the element under modification
The temporal coordinates of the version to be modified (vt and et, tt=now)
The new values of the validity and efficacy
Steps
Extend the timestamps of the selected version
Updates timestamps of the sibling versions
Updates timestamps of descendant and ancestor versions (if necessary)

11. The system architecture?
XML Document
XML Documents
Query
XML Documents
(Textual or Temporal Change)
Preprocessor
Query Processor
Update Processor
tnorms(ID,XML-DOC,PUBLICATION, VT-START,VT-END,TT-START,TT-END, ET-START,ET-END)
XML
repository
Inverted Index
Inherited timestamps are explicited at every level of the document hierarchy (in the preprocessing phase)
Timestamp attribute of tnorms have the same values of the timestamping tags associated with the contents tag
Inverted index built on title, heading and paragraph

12. Query processing Oracle 9i XML Engine Query XML Documents XML
FOR $a IN //article/title WHERE contains($a, ‘cereals’) RETURN const-tree(document($a), VALID CONTAINS now)
XML Documents
Preprocessing
Reconstruction
SELECT L.XML-DOC.extract(‘//article’).getStringVal() FROM tnorms L WHERE VT-START <= ‘07-NOV-2003’ AND VT-END >= ‘07-NOV-2003’
AND TT-START … AND ET-START …
AND CONTAINS(L.XML-DOC, ‘cereals WITHIN title’)>0
const-tree(document($a), VALID CONTAINS now AND TRANSACTION …)
Oracle 9i XML Engine
tnorms(ID,XML-DOC,PUBLICATION, VT-START,VT-END,TT-START,TT-END, ET-START,ET-END)
XML
repository
Inverted Index

13. Evaluation benchmark Six different query types Three XML document sets
1000 documents (24MB)
2000 documents (50MB)
5000 documents (120MB)
Variable document size
min = 2KB
avg = 24KB
max = 125KB
Six different query types
Queries on keywords
Q1 – keywords in contents
Q2 – keywords in type and contents
Temporal queries
Q3 – conditions on publication, validity and transaction time
Mixed queries
Q4, Q5, Q6 – with keywords and temporal conditions

14. Performance evaluation
Preprocessing improves the performance of temporal queries (with a negligible overhead for non-temporal queries)
The inverted index is effective only when very selective keywords are specified
The introduction of temporal elements (instead of intervals) substantially improves the reconstruction phase by reducing document size and memory required
naïve approach, without preprocessing and metadata

15. Conclusions and Future Work
We defined a temporal XML data model which
Captures the dynamics of norms in time
Allows their multiple versions to be represented
Defines the interaction between temporal dimensions and the document structural hierarchy
Is equipped with three basic operators
We designed, implemented and evaluated a prototype built on top of a commercial DBMS
Future developments
Study of optimized implementation solutions (e.g. based on decomposition of XML documents, execution of structural joins, etc.)