Download Database Systems For XML Data Storing

VTT-MEMO-ADA-01
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SECOM Co., Ltd. / VTT Building and Transport
Yoshinobu Adachi
E-Mail: [email protected]
VTT-MEMO-ADA-01
Memorandum
Database Systems For XML Data Storing
2001/07/28
1.
INTRODUCTION..........................................................................................................................1
2.
VARIETY OF DATABASE SYSTEMS ............................................................................................1
2.1
2.2
3.
RELATIONAL DATABASE .............................................................................................................1
XML NATIVE DATABASE ............................................................................................................2
OBSERVATION.............................................................................................................................2
1. Introduction
This document describes about database systems for XML data storing. In IFC Model Server project, the IFC
model data should be getting along with XML processing, therefore this document focuses on XML oriented
database systems.
2. Variety of Database Systems
At this moment, there are mainly two types of database system in order to store XML data. First one is the
relational database that stores XML data by mapping XML data structure to relational data structure, and second
one is the XML native database system.
2.1 Relational Database
The relational database that supports XML has following features:
§ XML data importing and exporting functionality
§ In general, the XML data is mapped to database table by relationship between specific tag element and
specific column in the table.
§ After storing the XML data in the relational database, following operations such as exclusion control,
search, back up management will be easy.
§ There is a need to manage the XML characteristic information, i.e. character code, namespace,
parent-child and forward-back relationship between tag elements. This means that it is not easy to get
completely same XML data after storing the XML data into tables.
§ BLOB is one possibility to store the whole XML data directly. However, only whole text search can be
usually used for searching the content in the BLOB.
Here are famous relational database systems that support XML functionality:
1. SQL Server 2000 – Microsoft:
SQL Server 2000 supports mainly exporting the data in the table as XML format. You can get
the SQL select results as XML format. The SQL command “SELECT” supports “FOR XML”
option for select operation. Basically the name of column in a table is used for the name of tag
in the XML data. XML View functionality is also implemented to be able to use XPath for
select operation. In XML View, the table or view looks like XML data, so you can use XPath to
select the data.
It is not necessary to install any optional software to support XML in SQL Server 2000.
SECOM Co., Ltd. Intelligent Systems Lab.
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2. Oracle8i – Oracle:
XML Developer’s Kit (XDK) is included in Oracle8i. XDK contains XML parser, XSLT engine,
XML importing and exporting modules. XML SQL Utility for Java enables to get the select
result as XML data. This utility is Java classes, so the functionality is called from Java applet
with JDBC.
3. DB2 UDB – IBM:
XML Extender extends DB2 UDB for XML support. XML Extender stores XML data into
tables and makes indexes for the XML elements and attributes, and search for the indexes is
available.
2.2 XML Native Database
XML native database means that the database can store XML data itself in the database or minimal changed
XML format in it, and it can export the stored XML data as completely same content. The XML native database
has following features:
§ Indexing for the XML data
§ Transforming to DOM tree.
§ XML data searching and updating
§ There seems no standard inquiring language like SQL. W3C is developing inquiry language.
Well known XML native database systems are shown below:
1. Tamino – Software AG:
Tamino stores XML data directly in the database and makes index automatically. Tamino does
not transform the XML data to other format like DOM tree, so it can output the XML data so
fast. Tamino includes SQL engine as well, and it can extract stored XML data content as
relational data structure.
2. Yggdrasill – Media Fusion:
Yggdrasill also stores XML data as its own structure directly and indexes are saved
automatically. The original inquiring language XBath is used for searching functionality. COM
API is supported, so it is available to use from C++, VB.
3. eXcelon – Excelon:
eXcelon is based on Object Oriented database system. The XML data is decomposed to nodes
as DOM tree structure.
3. Observation
To store XML data, relational database systems and XML native database systems are now available. Table 1
shows the comparison of relational database and XML native database.
Table 1. Comparison between Relational and XML native database
Functionality
Relational Database
XML Native Database
XML data reproduction performance
Inquiring language
Not good
SQL
Good
Not standardized
Inquiring language compatibility
Good
Not good
Product availability
Good
Average
The relational database has to manage mapping procedure to import and export the XML data, therefore there is
a need to develop some mapping logic and to define the table for specific XML data schema. After storing XML
data into table, it is available to use strong SQL functionality to search and select the partial data. This is one
advantage of relational database.
On the other hand, XML native database is very natural to handle XML document. The inquiring language is
not standardized at this moment, but W3C is developing such language.
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To consider about IFC model, the schema definition is written in EXPRESS language and it has very clear data
structure. The clear data structure enables following procedures:
§ Defining a consistent table design in relational database
§ Defining a consistent logic to access the data in the table
§ Defining a DOM tree structure
§ Defining a consistent logic to access the data in the DOM tree
It seems that the XML data reproduction is not so important, if the table covers whole IFC model schema
information completely.
SECOM Co., Ltd. Intelligent Systems Lab.