1. XML과 Database
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2. 차례 Database, Web, and XML XML Database Systems Data Models
Query Language and Processing
Storage and Index
Other issues
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3. Database and Web, before XML
DB : a back-end server for Web Applications
CGI
JDBC
Embedded SQL
Web
Information Retrieval
Target to manage (Web DB)
Thin Client
Scripts
Middle Tier
HTML
Web Server
Template Engine
Scripts
HTML Templates
Application Server
Application Code
Mapping Code
Back End
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4. XML eXtensible Markup Language
A new emerging standard for data representation and exchange on the internet
See the XML catalog ,
Separating content from presentation
Easy to provide multiple view of the same data
Easily parsed and self-describing
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5. XML Extensible — a dynamic data model
Simple — human-readable, easy to use
Flexible — for handling complex data
Portable — for cross-platform data exchange
Standard — easy to integrate, widely adopted
It is important that these points are clear. To understand these benefits is to understand the difference between different XML tools.
Most tools support the benefits at the top of the list, but to fully leverage XML, a tool has to support the entire list.
Simple: a data format that is as easy to use as HTML.
Extensible: the biggie - it is a dynamic data mode so that you are not locked into a rigid data model.
Flexible: Just because it is simple does not mean that it is limited. XML is flexible enough to handle all the complex data that today’s apps rely on including relationships and hierarchical info.
Portable: just like HTML and Java
Standard: all the benefits of standards (plug and play, easy to learn) apply here
BREAK FOR DEMO
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6. HTML과 XML 문서 비교
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7. Data mixed with presentation
XML Is All About Data
HTML example:
<heading1> Invoice </heading1>
<bold>To: Joe Bloggs <P>
From: J. Abrams <P>
Date: 2/1/1999<P>
Amount: $100 <P>
Tax: 21% <P>
Total $121 </bold>
Data mixed with presentation
Let’s illustrate the difference between HTML and XML, and demonstrate where HTML falls short.
Here is some HTML that shows an invoice from a guy named Joe. But if you look at the HTML, all that it can tell you is that “Joe” should be displayed in bold because (click) HTML mixes data with presentation.
This is why XML was born. (click) It comes to you from the World Wide Web Consortium (W3C), the same people who brought you HTML. This example shows you the same invoice in XML.
The first thing you will notice is that it is (click) human readable. It is ASCII so it is readable as well as portable.
Also, XML includes tags (click) so that even though I haven’t told you anything about this data in advance, you can read it and easily understand the data in this invoice. This is essential for sharing data over the Web.
But the killer feature of XML - XML Nirvana - is that XML is (click) extensible. If, all-of-a-sudden, you want to keep Joe’s address - no problem! You can easily add a new field to a single data object without disrupting any of your existing data. XML is a dynamic data model (!!), which means that you can easily expand to add new and unanticipated functions to your business or work with new partners. For database people: no schema evolution!!!
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8. XML Is All About Data Human Readable Comes with Tags XML example:
<Invoice>
<Customer> Joe Bloggs </Customer>
<From> J. Abrams </From>
<Date year=‘1999’ month=‘2’ day = ‘1’ />
<Amount unit = ‘Dollars’> 100 </Amount>
<TaxRate> 21 </TaxRate>
<Total currency = “Dollars”>121 </Total>
</Invoice>
Comes with Tags
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9. XML Is All About Data Extensible XML example: <Invoice>
<Customer>
<Name>Joe Bloggs </Name>
<Address> 25 Mall Road </Address>
</Customer>
<From> J. Abrams </From>
<Date year=‘1999’ month=‘2’ day = ‘1’ />
<Amount unit = ‘Dollars’> 100 </Amount>
<TaxRate> 21 </TaxRate>
<Total unit = “Dollars”>121 </Total>
</Invoice>
<Name>Joe Bloggs </Name>
<Address> 25 Mall Road </Address>
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10. XML Family of Standards
DOM (Document Object Model)
XML Namespaces
XSL (style language)
XQL (XSL query language)
XML Data / DCD / Schema
XUL (updates, future)
…many more
XML is more than just a data format, it comes with a family of interface standards for accessing and manipulating the data. The W3C continues to pump these out, with many new additions in the years to come. Object Design is a member of the W3C, and is actively involved with developing these standards.
So let’s take a look at some of these standards, which today’s tools must support to fully leverage XML:
XML is the data format standard
DOM is the API for writing apps on top of XML
XML Namespaces (recommended): how to differentiate between two tags of the same name but in different contexts. Such as the name of the book versus the name of the buyer of the book.
These three are recommended by the W3C (I.e. are standards today) and the following are still in the process of being finalized:
XSL: XML Style Language (2nd working draft) - lets you present the data in various styles - order the data, filter it (similar to a select statement).
XQL: XML Query language (draft) - a standard way of querying XML data (similar to SQL)
XML Data: ways of handling application (non-document) data. We are very involved with those committees at the W3C (target date for Proposed Recommendation is 9/99).
XUL: XML update language for updating an XML document at the element level. This is still just at the idea stage.
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11. Building Web Applications with XML
Thin Client
Scripts
Quickly react to changes
Lower maintenance costs
Does not depend on a single vendor
Middle Tier
HTML
Web Server / App Server
XSL
Application Code DOM
XML Server
Standard API and Template Language
XML
Back End
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12. Legacy DBs for XML Applications
XML as a new data-exchange format
for legacy DB applications
DB2XML
Transforming the results of database queries or complete databases into XML documents or into HTML documents using XSLT stylesheets.
DB2XML can be used:
as a standalone tool (with GUI or command line),
as a servlet to dynamically generate XML-documents
using the DB2XML API
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13. XML Database Systems 3 approaches Build special-purpose systems
Lore, Strudel
Best performance for XML data
Use object-oriented database systems
eXelon, Monet, Ozone
Object-oriented modeling
Use relational database systems
Oracle, Microsoft
Matured large market
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14. Lore Query Processor Data Engine Textual Interface Query Plan
Generator
Preprocessing
(Lorel2OQL)
Parsing
Applications
HTML GUI
Utilities
Query
Operators
Object
Manager
Optimizer
External Data
API
Physical
Storage
External,
Read-only
Data
Sources
queries
Non-query Requests
Query Processor
Data Engine
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15. eXelon
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16. Oracle 8i
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17. Data Models for XML XML is not a data model
Structure of an XML document
an ordered list of elements
each element
may have a set of attributes
may have (sub)elements (nested elements)
Structured data and full text mixed together
DOM defines how to translate an XML document into a data structure for processing
Need a true data model for XML data
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18. OEM: a Semi-structured Data Model
Object Exchange Model (Lore)
Semi-structured Data
Self-describing structure, the lack of schema
the structure changes rapidly and unpredictably
Labeled direct graph
Node : Object (OID) or atomic value (leaf)
Labeled Edge : object-subobject relationship
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19. OEM, an example <DBGroup> <Member Name=“유” Advisor=“m1”>
<Age>28</Age>
</Member>
<Member ID=“m1”, Project=“p1”>
<Name>박</Name>
<Advisor>홍</Advisor>
<Project ID=“p1” Member=“m1”>
<Title>XML DB</Title>
</Project>
</DBGroup>
DBGroup
&1
Member
Project
Member
&2
&3
&4
{Name=“Smith”,
Advisor=“m1”}
{ID=“m1,
Project=“p1”}
{ID=“p1,
Project=“m1”}
Age
Name
Advisor
Title
&5
&6
&7
&8
Text
Text
Text
Text
&12
&9
&10
&11
“28”
“박”
“홍”
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20. Issues in Data Modeling
How to simultaneously view XML information in both
a set of documents
a single large database
No loss of information in XML
How to represent the Ordering of elements
external/internal entities, processing instructions
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21. XML DB Design
When should attributes (subelements) be used?
Is a 1-to-1 relationship best represented using element nesting or IDREFs?
How to translate the conceptual model (OEM?) into an XML encoding?
Need to identify the relationship between DTDs and traditional DB schema
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22. Query Languages for XML DB
Requirements
Path Expressions
Queries over
the structured and semistructured data
full text
the mixture of data elements and full text
W3C, Query Languages for the Web, 1998
QL for semistructured data
Lorel, UnQL
XQL, XML-QL
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23. XML-QL
Syntax
Select <variable-list> where <XML-pattern>+
Example
select $n, $h
where <person> <age=$a>
<name> $n </name>
<address> 서울 성북구 동선동3가</address>
[<hobby> $h </hobby>]
</person>, $a > 18
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24. Issues in Query Processing
The true requirements for XML QL is not known
Need to review all facets of traditional query processing
Need to Develop a new IR model
proximity in XML documents
similarity measure between XML elements
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25. How to integrate Optimization Schemes
traditional (DB) query processing model and
information retrieval model
Optimization Schemes
for not well-structured XML data
for queries mixed with full text retrieval and structured/semistructured search
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26. Storage Structure and Indexing
Clustering schemes for storing XML data
New index types
for quickly finding certain elements, attributes, and more complex structural patterns
element orderings
Determine the level of parsing for storing XML documents
Based on the analysis of encoding pattern
merging identical text strings (sub-patterns) by using appropriate IDREFs
compression based on regular patterns
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27. Issues in Various DB Features
Full view support for XML
both virtual and materialized views
incremental maintenance
XSL as a view definition language
Data integrity issue
What are constraints on XML data?
key, referential, domain
How to represent the constraints
How to check them when changes occur
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28. Transaction Control over XML database Performance Evaluation
Trigger
active database capabilities in XML
Transaction Control over XML database
Performance Evaluation
need to make an appropriate benchmark for XML data
XML data set
query types
mix of queries and updates
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29. References Research issues Storing XML data into RDBMSs
Data Management for XML: Research Directions,
More on Data Management for XML,
Storing XML data into RDBMSs
A Performance Evaluation of Alternative Mapping Schemes for Storing XML Data in a Relational Database, ercim.inria. publications/RR-3680
XML Database Systems
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