April 24, 2006

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Demo of Scheme Implementation of the A-Priori Algorithm for Mining Association Rules

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• primarily involves two functions:
  • getCk: joins F_k-1 with itself to compute the candidate item sets of size k
  • getFk: queries C_k to compute the frequent items sets of size k
• Full source code is available here

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DTDs

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• a DTD (Document Type Definition) is a grammar for an XML document
• * (0 or more), + (one or more), ? (optional), and | (or) are DTD metacharacters
• DTD for instructor-course data
  
  

  <!ELEMENT instructor-course-data (instructor | course)*> <!ELEMENT instructor (name, ((office, address+) | (bldg, no)))> <!ATTLIST instructor iid ID #IMPLIED teaches IDREFS #IMPLIED> <!ELEMENT name (#PCDATA)> <!ELEMENT office (bldg, no)> <!ELEMENT address (street?, city, state, zip?)> <!ELEMENT street (#PCDATA)> <!ELEMENT city (#PCDATA)> <!ELEMENT state (#PCDATA)> <!ELEMENT zip (#PCDATA)> <!ELEMENT course (dept, no)> <!ATTLIST course cid ID #IMPLIED taught-by IDREFS #IMPLIED> <!ELEMENT dept (#PCDATA)> <!ELEMENT no (#PCDATA)>

  
  
• use comma to specify a sequence
  e.g., instructor and course elements may appear in any order in instructor-course-data while no must follow bldg in office
• a DTD can either be inlined into an XML document or factored into a separate file
• notice that a DTD is more expressive, and, thus, flexible, than a relational database schema
• to keep the DTD in a separate file, use the following preamble to your XML document:
  
  

  <?xml version="1.0"?> <!DOCTYPE instructor-course-data SYSTEM "icd.dtd">

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XSchema

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• XSchema (XML Schema) is a new standard for specifying XML document grammars
• it addresses some of the limitations of DTDs
  • in particular, XSchema
    • has support for data types, and
    • uses XML syntax (why would this be helpful?)
• XSchema for instructor-course data
  
  

  <?xml version="1.0"?> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.w3schools.com" xmlns="http://www.w3schools.com" elementFormDefault="qualified"> <xs:element name="instructor-course-data"> <xs:complexType> <xs:sequence> <xs:element name="instructor"> <xs:attribute name="iid" type="xs:integer"/> <xs:attribute name="teaches" type="xs:string"/> <xs:complexType> <xs:sequence> <xs:element name="name" type="xs:string"/> <xs:element name="office"> <xs:complexType> <xs:sequence> <xs:element name="bldg" type="xs:string"/> <xs:element name="no" type="xs:integer"/> </xs:sequence> </xs:complexType> </xs:element> <xs:element name="address"> <xs:complexType> <xs:sequence> <xs:element name="street" type="xs:string"/> <xs:element name="city" type="xs:string"/> <xs:element name="state" type="xs:string"/> <xs:element name="zip" type="xs:integer"/> </xs:sequence> </xs:complexType> </xs:element> </xs:sequence> </xs:complexType> </xs:element> <xs:element name="course"> <xs:complexType> <xs:sequence> <xs:element name="dept" type="xs:string"/> <xs:element name="no" type="xs:integer"/> </xs:sequence> </xs:complexType> </xs:element> </xs:sequence> </xs:complexType> </xs:element> </xs:schema>

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Yacc for XML?

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• DTDs and XSchemas are grammars for XML documents
• we could develop a program generator which takes a grammar as input and automatically produces a program to process XML documents conforming to that grammar
• since an XSchema is an XML document, we can develop our program generator as an XSLT stylesheet and use an XSLT processor to facilitate the program generation
  • XSLT to come ....
  • program generation is a powerful idea (and abstraction) which applies to many areas of computer science
  • akin to YACC

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Mining for Schema

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• another application of data mining
• mining for schema in semistructured data [NAM]
• given a set of XML documents, mine for a DTD or XSchema
  • XTRACT is a system developed at Bell Laboratories which mines a DTD from a set of XML documents [XTRACT]
• given n mined schemas, how can we evaluate which is best?
  • develop metrics like excess and deficit [NAM]

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XML Suite of Technologies and Tools

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XML has matured from simple text markup for data interchange to a mature technology with a rich suite of associated tools. While these tools are beyond the scope of this lecture, below we provide references to a few and encourage you to explore them.

• SAX and DOM
  • SAX (Simple API for XML) is a syntax-driven standard for parsing XML data
    • it provides a simple, easy to use API for manipulating XML
  • DOM (Document Object Model) is also an API for XML
    • DOM is object-oriented and reads the entire XML document and construct a parse tree from it
• Cascading Stylesheets (CSS)
• XSL (eXtensible Stylesheet Language) is a language for expressing stylesheets
• it consists of three parts:
  • XSLT (XSL Transformations)
  • XPath (the XML Path language)
  • XSL FO (XSL Formatting Objects)
• RDF (Resource Description Framework) is a proposal for representing metadata in XML
  • it has its own data model and syntax
  • a way to make declarations about a resource and connect those declarations to derive meaning
  • has been a key ingredient in the W3C's vision of the semantic web
  • the structure and content of the Open Directory Project, a popular human-compiled directory of the web, are described in RDF
  • what is RDF?
• XHTML (Extensible HyperText Markup Language)
  • HTML is not XML
    • while all tags in XML must be closed, some tags in HTML need not be closed (e.g., <br>, <li>, or <p>)
    Furthermore, HTML is not case-sensitive; XML is case-sensitive.
  • a W3C initiative for HTML in XML
  • a language which describes document presentation in XML
• XML Tools
• XML Editors

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Cascading Stylesheets (CSS)

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XML is not very useful in isolation. In order to view XML, it needs to be converted into HTML. There are two methods for this conversion: CSS (Cascading Style Sheets) and XSL (eXtensible Stylesheet Language). CSS does not actually perform an explicit conversion from XML to HTML. It is rather a lightweight method which associates each element with a style of presentation. Click here for a nice page on the differences between CSS and XSLT. The following CSS code specifies how a browser should render the books.xml (courtesy O'Reilly Mozilla DevCenter).

books {
    display:block;
    height:200px;
    width:280px;
    border:1px solid #000;
    overflow:auto;
    background-color:#eee;
    font: 12px verdana;
}

book {
   display: block;
   padding:10px;
   margin-bottom:10px;
   border-top:1px solid #ccc;
   border-bottom:1px solid #ccc;
   background-color:#fff;
}

CSS permits multiple presentations for the same document.

To associate an XML document with a CSS, use the following element after the <?xml version="1.0"?> in the XML document.

<?xml-stylesheet href="books.css" type="text/css"?>

To associate an HTML document with a CSS, use the following element within the <head> element of the HTML document:

<link rel="stylesheet" href="homepage.css" type="text/css">

CSS can now be used to do some pretty slick rendering. Illustration of HTML list where list items appear to be images.

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Simple Example of Adding a CSS to HTML

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body {
   background-color: E0F7F0; 
}

h1 {font-weight: bold;
    text-align: left;
    color: black;
    font-family: "Verdana", Arial, sans-serif}

/* unvisited links */
a:link {color: #CC9933;
        size: 3;
        font-family: Verdana, Arial, Helvetica, sans-serif}

<html>

<head>
<title>A simple webpage</title>
<link rel="stylesheet" href="homepage.css" type="text/css">
</head>

<h1>Header 1</h1>

<a href="http://espn.com">ESPN.com</a>

</html>

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Files Used In Class

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• icd.dtd (DTD for instructor-course data)
• icd4.xml (instructor-course data with reference to its DTD)
• icd.xsd (XSchema for instructor-course data)
• icd5.xml (instructor-course data with reference to its XSchema)
• books.css (CSS for books XML data)
• books.xml (books data with reference to a CSS)
• homepage.css (CSS for simple webpage)
• index.html (simple webpage with reference to a CSS)

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References

[CSS]	S. Callihan. Cascading Style Sheets (CSS) by Example. Que, 2001.
[DBCB]	H. Garcia-Molina, J. D. Ullman, and J. Widom. Database Systems: The Complete Book. Prentice Hall, 2002.
[DMXD]	S. S. Chawathe. Describing and Manipulating XML Data. Bulletin of the IEEE Computer Society Technical Committee on Data Engineering, Vol. 22, No. 3, pp. 3-9, September 1999.
[DOM]	J. Marini. The Document Object Model: Processing Structured Documents . Osborne/McGraw-Hill, 2002.
[LXML]	E. T. Ray. Learning XML. O'Reilly, Second edition, 2003.
[NAM]	S. Nestorov, S. Abiteboul, and R. Motwani. Extracting Schema from Semistructured Data. In Proceedings of the ACM International Conference on Management of Data (SIGMOD), pp. 295-306, 1998.
[XTRACT]	M. Garofalakis, A. Gionis, R. Rastogi, S. Seshadri, and K. Shim. XTRACT: A System for Extracting Document Type Descriptors from XML Documents. In Proceedings of the ACM International Conference on Management of Data (SIGMOD), pp. 165-176, 2000.