Transcript XXX-xml - Rose

XML
Salman Azhar
Semi-structured Data
XML (Extensible Markup Language)
Well-formed and Valid XML
Document Type Definitions
IDs and IDREFs
These slides use some figures, definitions, and explanations from ElmasriNavathe’s Fundamentals of Database Systems
and Molina-Ullman-Widom’s Database Systems
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Framework
1.
Information Integration :

2.
Semi-structured Data :

3.
Making databases from various places work as
one.
A new data model designed to cope with
problems of information integration.
XML :

A standard language for describing semistructured data schemas and representing data.
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1. Information Integration

Generally databases in an enterprises have:

Several underlying database management
systems



Oracle,
Informix,
MS SQL Server,
Sybase (SQL Server),
DB2,
MS Access, etc.
Several underlying database schemas

Information in an employee table can contain



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Employee Name, SSN, DOB, title, hrsPerWeek.
modifiedTime, modifiedBy
Employee Name, SSN, DOB, title, degree, createTime,
createBy
Employee Name, SSN, DOB, title, salary, modifiedTime,
modifiedBy, createTime, createBy
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2. Semi-structured Data

A new data model designed to
cope with problems of information
integration

Accommodates of different DBMS



Oracle,
Informix,
MS SQL Server,
Sybase (SQL Server),
DB2,
MS Access, etc.
Integrates different schemas



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Employee Name, SSN, DOB, title, hrsPerWeek, modifiedTime, modifiedBy
Employee Name, SSN, DOB, title, degree, createTime, createBy
Employee Name, SSN, DOB, title, salary, createTime, createBy, modifiedTime,
modifiedBy
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3. XML

A standard language for describing
semi-structured data schemas and
representing data.
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The Information-Integration
Problem
Major bottleneck in enterprise
application integration


For example…

Hewlett Packard split into HP and Agilent


HP bought Compaq
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Need to separate data into different destinations
Need to integrate data from different sources
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The Information-Integration
Problem
Related data exists in many places and
could, in principle, work together.
But different databases differ in:


Model
1.
relational, object-oriented?

Schema
2.
normalized/denormalized?

Terminology
3.

are consultants employees? Retirees?
Subcontractors?
Conventions
4.

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meters versus feet?
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Example

Consider merger of two stores in a Mall


may be some overlap in the products sold
but the databases are different
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Example

Each company has a database

One may use a relational DBMS


One stores the phones of distributors,


the other does not
One distinguishes products in one department


the other keeps the data in an MS-Word document
the other doesn’t
One counts inventory by number of items,

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the other by cases
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Two Approaches to Integration
1.
Warehousing

Makes a copy of the data

2.
More developed of the two
Mediation

Creates a view of the data

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Newer and less developed
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Warehouse Diagram
User query
Result
Warehouse
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Wrapper
Wrapper
Source 1
Source 2
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A Mediator
Result
User query
Mediator
Query
Result
Result
Wrapper
Query
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Wrapper
Result
Source 1
Query
Query
Result
Source 2
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Warehousing
Make copies of the data sources at a central
site and transform it to a common schema




Reconstruct data daily/weekly
Do not try to keep it more up-to-date than that.
Pro:



very well-developed
several commercial tools are available
Con:


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data can be old since updates are expensive
24-hour availability threatened by large data updates
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Mediation
Create a view of all sources, as if they were
integrated



Answers a view query by translating it to
terminology of the sources and querying them
Pro:


Current data
Con:


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Can be slow as it requires real time merger of different
data sources
Lack of tools available
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Warehouse Diagram
User query
Result
Warehouse
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Wrapper
Wrapper
Source 1
Source 2
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A Mediator
Result
User query
Mediator
Query
Result
Result
Wrapper
Query
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Wrapper
Result
Source 1
Query
Query
Result
Source 2
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Semi-structured: Motivation

Most effective approach to Information
Integration:


Semi-structured Data Model
or Semi-structured Objects
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Semi-structured: Motivation

Main limitation of Object-Oriented
Models:

Object Models are Strongly Typed


Objects of a class have one structure only
Semi-structured approach solves this
problem
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Semi-structured Data

Purpose:

Represent data from independent sources
more flexibly than


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either relational
or object-oriented models
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Semi-structured Data

Each object has a class of their own and
properties are defined whatever labels
are attached to that object

Properties mean



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attributes,
relationships,
methods, etc.
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Semi-structured Data

Think of objects

but with the type of each object is the
objects its own business


not that of its “class”
Labels to indicate meaning of
substructures
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Semi-structured Graphs

Easy to think of Semi-structured data as
Graphs


Nodes = objects
Labels on arcs =


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attributes leading to a leaf node
relationships leading to another node
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Semi-structured Graphs

Atomic values at leaf nodes


nodes with no arcs out
Flexibility: no restriction on…


labels out of a node
number of successors with a given label
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Example: Data Graph
Root object represents the entire DB. Often look like trees, but are not.
root
The
restaurant
object for KFC
(arc-in called
rest; arc-out
labeled name
to KFC)
soda
rest
soda
manf
name
sellsAt
manf
PepsiCo
prize
name
year
Pepsi
Sobe
name
addr
KFC
Main St
Notice a
new kind
of data.
2003
award
BestSeller
The soda object for Pepsi
(arc-in called soda;
arc-out called name to Pepsi)
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Stage is Now Set for XML

A technology has application to
different situations


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foundations remain the same
applications changes
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Extensible Markup Language
(XML)

XML


HTML


uses tags for semantics (e.g., “this is an address”)
uses tags for formatting (e.g., “italic”),
Key idea:


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create tag sets for a domain (e.g., genomics)
translate all data into properly tagged XML docs
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Well-Formed and Valid XML

Well-Formed XML

allows you to invent your own tags


similar to labels in semi-structured data graph
Valid XML


involves a DTD (Document Type Definition)
DTD gives


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a grammar for the use of labels
limits the set of labels our of node
the order and number of times a label occurs
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Well-Formed XML

All XML documents have



Header defines



Header
Body
version
specifies that the document is in well-formed XML
Body can include


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root tag
several properly matching tags
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Well-Formed XML: Header

Start the document with a declaration


surrounded by <? … ?> .
Normal declaration for Well-Formed
XML is:
<? XML VERSION = “1.0” STANDALONE = “yes” ?>


Version indicates version number
Standalone = “yes” means no DTD

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no DTD means well-formed XML
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Well-Formed XML: Body

Body of document is a root tag
surrounding nested tags.

Body can include:

several properly matching tags


special tag called root tag

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(as in html structure)
can have a special meaning such as document type
or can be generic
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Tags

Tags, as in HTML

are normally matched pairs, as



may be nested arbitrarily
some tags requiring no matching ending


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<BLAH> … </BLAH>
such as <P> in HTML, are also permitted
however, we will not use these in examples
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Example: Well-Formed XML
<? XML VERSION = “1.0” STANDALONE = “yes” ?>
<RESTS>
<REST>
<NAME>Taco Bell</NAME>
One of several nested
<SODA><NAME>Pepsi</NAME>
REST tags representing
<PRICE>1.00</PRICE></ SODA>
information about a
<SODA><NAME>Sobe</NAME>
single REST
<PRICE>2.00</PRICE></SODA>
<NAME> tag specifies </REST >
the REST name
<REST> … <SODA> tags
Literal Data items
have
names
</REST >
are contained at
and
price
for
the atomic level
…
each Soda
</RESTS>
Root tag RESTS
surrounds the
entire document
nested in
<NAME> and
<PRICE> tags
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XML and Semi-structured Data

Consider this…

Is Well-Formed XML documents with
nested tags is exactly the same idea as
trees of semi-structured data?

Tags


Nodes


represent data between matching tags
Parent-child relationship

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are the labels on edges
is immediate nesting in XML
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XML and Semi-structured Data


Semi-structured approach allows for
non-tree structures
We shall see that XML also enables nontree structures

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mimics the semi-structured data model
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Group Exercise

Convert the following into a Semistructured representation
<? XML VERSION = “1.0” STANDALONE = “yes” ?>
<RESTS>
<REST>
<NAME>Taco Bell</NAME>
<SODA><NAME>Pepsi</NAME>
<PRICE>1.00</PRICE></ SODA>
<SODA><NAME>Sobe</NAME>
<PRICE>2.00</PRICE></SODA>
</REST >
<REST> …
Note: Do not turn over to the
</REST >
next page before attempting
…
</RESTS>
this exercise yourself!
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Solution:
The semi-structured representation
<? XML VERSION = “1.0” STANDALONE = “yes”
?>
<RESTS>
<REST>
<NAME>Taco Bell</NAME>
RESTS
<SODA><NAME>Pepsi</NAME>
<PRICE>1.00</PRICE></ SODA>
<SODA><NAME>Sobe</NAME>
<PRICE>2.00</PRICE></SODA> REST
</REST >
<REST> …
</REST >
NAME
…
SODA
</RESTS>
REST
REST
SODA
Taco Bell
NAME
Pepsi
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PRICE
1.00
NAME
Sobe
PRICE
...
Note: Data is
stored in leaf
nodes and
structure (tags)
in internal nodes
2.00
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Valid XML

Switching gears: Well-formed to Valid XML



Valid XML is the most interesting use of XML
Essentially a context-free grammar for describing
XML tags and their nesting
Specified by DTD

Each domain of interest creates one DTD that
describes all the documents this group will share

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For example, electronic components, travel industry, etc.,
will have their own DTDs
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DTD Structure
Note: !DOCTYPE is key word
with <root tag> being the
name of DOCTYPE
<!DOCTYPE <root tag> [
<!ELEMENT <name> ( <components> )
<more elements>
]>
Between [ … ] list of ELEMENT definition
Each !ELEMENT has a <name> with the allowed
list of <components> usually in the order listed
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DTD Elements

Element definition consists


of its name (tag)
and a parenthesized description of any
nested tags



includes order of subtags
and their multiplicity (0, 1, or many times)
Leaves (text elements)

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have #PCDATA in place of nested tags
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Example: DTD
<!DOCTYPE RESTS [
RESTS can have * (0
or more) REST
<!ELEMENT RESTS (REST*)>
REST has NAME and
<!ELEMENT REST (RNAME, SODA+)>then + (1 or more)
SODA… Order
matters!
<!ELEMENT NAME (#PCDATA)>
SODA has NAME followed PRICE
SODA’s NAME and PRICE are data (#PCDATA)
NAME and PRICE are
data (#PCDATA): No
more tags just text
GROUP EXERCISE: COMPLETE THE DTD
]>
Note: Do not turn over to the next page before attempting
this exercise yourself!
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Example: DTD
<!DOCTYPE RESTS [
RESTS can have * (0
or more) REST
<!ELEMENT RESTS (REST*)>
REST has NAME and
<!ELEMENT REST (RNAME, SODA+)>then + (1 or more)
SODA… Order
matters!
<!ELEMENT NAME (#PCDATA)>
<!ELEMENT SODA (NAME, PRICE)> NAME and PRICE are
data (#PCDATA): No
more tags just text
<!ELEMENT NAME (#PCDATA)>
<!ELEMENT PRICE (#PCDATA)>
SODA has NAME
followed PRICE
]>
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Element Descriptions Rules


Subtags must appear in order shown
A tag may be followed by a symbol to
indicate its multiplicity:





Identical to UNIX regular expressions.
* = zero or more.
+ = one or more.
? = zero or one.
Alternative sequences of tags can be
connected by

the symbol |
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Example: Element Description

A name is


Either an optional title (e.g., “Dr.”), a first
name, and a last name, in that order,
or it is an IP address
<!ELEMENT NAME (
(TITLE?, FIRST, LAST) | IPADDR
Alternative symbol
)>
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Use of DTDs
In order to specify a document follows
a particular DTD

1.
Set STANDALONE = “no”
a)
b)
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Either include the DTD as a preamble of the
XML document
Follow DOCTYPE and the <root tag> by
SYSTEM and a path to the file where the DTD
is stored
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Example (a)
<? XML VERSION = “1.0” STANDALONE = “no” ?>
<!DOCTYPE RESTS [
DTD
<!ELEMENT RESTS (REST*)>
<!ELEMENT REST (NAME, SODA+)>
<!ELEMENT NAME (#PCDATA)>
<!ELEMENT SODA (NAME, PRICE)>
<!ELEMENT NAME (#PCDATA)>
<!ELEMENT PRICE (#PCDATA)>
]>
Document
<RESTS>
Same as earlier but this time it conforms to the above DTD
<REST>
<NAME>Taco Bell</NAME>
<SODA><NAME>Pepsi</NAME> <PRICE>1.00</PRICE></ SODA>
<SODA><NAME>Sobe</NAME> <PRICE>2.00</PRICE></SODA>
</REST >
<REST> …
</REST >
…
</RESTS>
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Example (b)

Assume the RESTS DTD is in file rest.dtd
<? XML VERSION = “1.0” STANDALONE = “no” ?>
Get the DTD
<!DOCTYPE Rests SYSTEM “rest.dtd”>
<RESTS>
<REST>
<NAME>Taco Bell</NAME>
<SODA><NAME>Pepsi</NAME>
<PRICE>1.00</PRICE></ SODA>
<SODA><NAME>Sobe</NAME>
<PRICE>2.00</PRICE></SODA>
</REST >
<REST> …
</REST >
…
</RESTS>
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from the file
rest.dtd
Document
Same as
earlier but
this time it
conforms to
the DTD in
rest.dtd
46
Attributes


Attributes are another important component
of DTD and XML docs
Opening tags in XML can have attributes


like <A HREF = “…”> in HTML
In DTD <!ATTLIST <elementname>… >

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gives a list of attributes and their data types for
this element
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Example: Attributes

Rests can have an attribute kind

which is either qsr, family, or other.
The element definition is unchanged
 However, we add an ATTLIST.
<!ELEMENT REST (NAME SODA*)>
<!ATTLIST REST kind “qsr” |
“family” | “other”>

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Example: Attribute Use
In a document that allows REST tags, we might
see:
<REST kind = “qsr”> New info: kind = “qsr”
<NAME>KFC</NAME>
<SODA><NAME>Pepsi</NAME>
<PRICE>1.00</PRICE></SODA>
...
</REST>

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IDs and IDREFs


Introduce links from one object to another
Allows the structure of an XML document to
be a general graph


rather than just a tree.
These are pointers from one object to
another

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in analogy to HTML’s NAME = “blah” and HREF =
“#blah”
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Creating IDs


We give an element Elephant an
attribute Attention of type ID in the
DTD
When using tag <Elephant> in an XML
document, give its attribute Attention a
unique value.

For example,

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<Elephant
Attention = “213”>
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Creating IDREFs

IDREFs are similar to IDs:

To allow objects of type Fig to refer to
another object with an ID attribute,


Or, let the attribute have type IDREFS,

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give Fig an attribute of type IDREF (single
string of type ID)
so the Fig –object can refer to any number of
other objects (any number strings of type ID).
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Example: IDs and IDREFs

Let us redesign our RESTS DTD to include
both REST and SODA sub-elements


Both rests and sodas will have ID attributes called
name
Rests have PRICE sub-objects,


Sodas have attribute soldBy,

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consisting of a number (the price of one soda) and an
IDREF theSoda leading to that soda
which is an IDREFS leading to all the rests that sell it
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The DTD
RESTS have 0+
REST and 0+ SODA
<!DOCTYPE Rests [
<!ELEMENT RESTS (REST*, SODA*)>
REST objects have name as an
<!ELEMENT REST (PRICE+)>
ID attribute and have one or
more PRICE sub-objects
<!ATTLIST REST name ID>
PRICE objects <!ELEMENT PRICE (#PCDATA)>
have a
<!ATTLIST PRICE theSoda IDREF>
number (the
price) and
<!ELEMENT SODA ()>
one reference
to a soda
<!ATTLIST SODA name ID, soldBy IDREFS>
]>
Soda objects have an ID attribute called name,
and a soldBy attribute that is a set of Rest names
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Example Document
<RESTS>
<REST name = “Taco Bell”>
<PRICE theSoda = “Pepsi”>1.00</PRICE>
<PRICE theSoda = “Sobe”>2.00</PRICE>
</REST> …
<SODA name = “Pepsi”, soldBy = “KFC,
TacoBell,…”>
</SODA> …
</RESTS>
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<!DOCTYPE Rests [
<!ELEMENT RESTS (REST*, SODA*)>
<!ELEMENT REST (PRICE+)>
<!ATTLIST REST name ID>
<!ELEMENT PRICE (#PCDATA)>
<!ATTLIST PRICE theSoda
IDREF>
<!ELEMENT SODA ()>
<!ATTLIST SODA name ID,
soldBy IDREFS>
]>
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Recap





Semi-structured Data
XML (Extensible Markup Language)
Well-formed and Valid XML
Document Type Definitions
IDs and IDREFs
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Perspective

Here XML is used as a EDI medium


EDI = electronic data interchange
There are many other using for XML

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Each has its own utilization
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Questions?
Questions???


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Doesn’t mean you will get all the answers! 
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