1 New Ways of Querying the Web by Eliahu Brodsky and Alina Blizhovsky

2 Simple Querying A search engine looks for the word (or the words) that a document contains. A search engine looks for a Web document which contains the word.

3 Querying structured data A data on the Web may be structured (e.g. books catalog). A “structure” means schema. The schema may not be rigid (semi- structured data). More complex queries may be executed.

4 CGI Advantage –Uses the existing DBMS (e.g. relational). Disadvantage –Problems on integrating a data from the different Web sources.

5 XML (Extensible Markup Language) A subset of SGML Benefits –Arbitrary extension of a document’s tags and attributes. –Support for documents with complex structure. –Validation of documents structure (with respect to an optional Document Type Descriptor).

6 Example of XML data Database Systems Date Addison-Wesley The Math Works MATLAB

7 Example of Document Type Descriptor (DTD) <!ELEMENT book (title,author?,publisher)>

8 Semi-structured Data Model Non-rigid schema Object Exchange Model (OEM) Data represented by a graph.

9 Example of XML data Database Systems Date Addison-Wesley The Math Works MATLAB

10 book (year=“1995”) (year=“1998”) title author name publisher Database Systems Addison- Wesley Date publisher title MATLAB The Math Works

11 Example of XML data Database Systems Date Addison-Wesley The Math Works MATLAB

12 book (year=“1995”) (year=“1998”) title author name publisher Database Systems Addison- Wesley Date publisher title MATLAB The Math Works related

13 XML-QL Extracts data from large XML documents. Integrates XML data from multiple sources. Translates XML data between different DTD. Processes a request by –sending queries to XML sources, or by –transporting large amounts of XML data to clients.

14 Example of XML-QL WHERE Addison-Wesley $t IN “ CONSTRUCT $t

15 Example of XML data Database Systems Date Addison-Wesley The Math Works MATLAB

16 Result of the query Database Systems

17 WHERE Addison-Wesley $a1 IN “ The Math Works $a2 IN “ $a1 = $a2 CONSTRUCT $a1

18 Regular Path Expressions Permitted wherever XML permits an element. Provide: –alternation ( | ) –concatenation (. ) –Kleene-star operators ( * )

19 Example of a regular path expression WHERE $r IN “ CONSTRUCT $r

20 $r.

21 XQL Is designed specifically for XML documents. Provides a simple syntax (patterns modeled after directory notation). Expressed in strings that can be embedded in programs, scripts, and XML or HTML attributes.

22 The Result of XQL Query Depends on implementation. One of the following: –XML document. –A tree that can be fed back in to XQL. –Different type of structure (e.g. set of pointers to nodes).

23 Search Context Is the set of nodes against which a query operates. The “root context” and the “current context”: / use the “root context”. / use the “current context” explicitly

24 Example of an XQL = = Find all books where the value of style attribute of the book is equal to the value of the specialty attribute of the bookstore element at the root of the XML document.

25 Additional examples author[lastname = ‘Bob’] Find all author elements whose last name sub element is Bob. author[. = ‘Bob’] Find all author elements whose value is Bob.

26 Regular path expressions in XQL bookstore//title Find all title elements, one or more levels deep in the bookstore. bookstore/*/title Find all title elements that are grandchildren of bookstore elements.

27 Indices in XQL Text1 Text2 Text3 Text4 x/y[0] Text1,Text3 (x/y)[3] Text4 x[1]/y[0] Text3

28 XML-QL vs. XQL XQL may easily be embedded into programs, scripts, XML and HTML tags. XQL assume the user understand XML document as a graph. XML-QL provides construction of new complicated XML documents. XML-QL provides XML-like patterns.