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XML and Databases

XML and Databases. Outline (ambitious). Background: documents (SGML/HTML) and databases (structured and semistructured data) XML Basics and Document Type Descriptors XML query languages: XML-QL and XSL. XML additions: Xlink, Xpointer, RDF, SOX, XML-Data Document Object Model (XML API's).

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XML and Databases

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  1. XML and Databases

  2. Outline (ambitious) • Background: documents (SGML/HTML) and databases (structured and semistructured data) • XML Basics and Document Type Descriptors • XML query languages: XML-QL and XSL. • XML additions: Xlink, Xpointer, RDF, SOX, XML-Data • Document Object Model (XML API's)

  3. Some Useful Articles XML, Java, and the future of the web http://webreview.com/wr/pub/97/12/19/xml/index.html XML and the Second-Generation Web http://www.sciam.com/1999/0599issue/0599bosak.html Articles/standards for XML, XSL, XML-QL http://www.w3c.org/ http://www.w3.org/TR/REC-xml

  4. Background What’s the difference between the world of documents and information retrieval and databases and query interfaces?

  5. Document world > plenty of small documents > usually static > implicit structure section, paragraph, toc, > tagging > human friendly > content form/layout, annotation > Paradigms “Save as”, wysiwyg > meta-data author name, date, subject Database world > a few large databases > usually dynamic > explicit structure (schema) > records > machine friendly > content schema, data, methods > Paradigms Atomicity, Concurrency, Isolation, Durability > meta-data schema description Documents vs Databases

  6. Documents editing printing spell-checking counting words retrieving (IR) searching Database updating cleaning querying composing/transforming What to do with them

  7. HTML • Publishing hypertext on the World Wide Web • Designed to describe how a Web browser should arrange text, images and push-buttons on a page. • Easy to learn, but does not convey structure. • Fixed tag set. Text (PCDATA) Opening tag • <HTML> • <HEAD><TITLE>Welcome to the XML course</TITLE></HEAD> • <BODY> • <H1>Introduction</H1> • <IMGSRC=”dragon.jpeg"WIDTH="200"HEIGHT="150” > • </BODY> • </HTML> Closing tag “Bachelor” tag Attribute name Attribute value

  8. The Structure of XML • XML consists of tags and text • Tags come in pairs<date> ...</date> • They must be properly nested <date> <day> ... </day> ... </date> --- good <date><day> ... </date>... </day> --- bad (You can’t do <i> ... <b> ... </i> ...</b> in HTML)

  9. XML text XML has only one “basic” type -- text. It is bounded by tags e.g. <title> The Big Sleep </title> <year> 1935 </ year> --- 1935 is still text XML text is called PCDATA (for parsed character data). It uses a 16-bit encoding, e.g. \&\#x0152 for the Hebrew letter Mem Later we shall see how new types are specified by XML-data

  10. XML structure Nesting tags can be used to express various structures. E.g. A tuple (record) : <person> <name>Malcolm Atchison</name> <tel>(215) 898 4321</tel> <email>mp@dcs.gla.ac.sc</email> </person>

  11. XML structure (cont.) • We can represent a list by using the same tag repeatedly: <addresses> <person> ... </person> <person> ... </person> <person> ... </person> ... </addresses>

  12. Terminology The segment of an XML document between an opening and a corresponding closing tag is called an element. <person> <name> Malcolm Atchison </name> <tel> (215) 898 4321 </tel> <tel> (215) 898 4321 </tel> <email> mp@dcs.gla.ac.sc </email> </person> element element, a sub-element of not an element

  13. person name tel tel email XML is tree-like Malcolm Atchison (215) 898 4321 (215) 898 4321 mp@dcs.gla.ac.sc Semistructured data models typically put the labels on the edges

  14. Mixed Content An element may contain a mixture of sub-elements and PCDATA <airline> <name> British Airways </name> <motto> World’s <dubious> favorite</dubious> airline </motto> </airline> Data of this form is not typically generated from databases. It is needed for consistency with HTML

  15. A Complete XML Document <?xmlversion="1.0"?> <person> <name> Malcolm Atchison </name> <tel> (215) 898 4321 </tel> <email> mp@dcs.gla.ac.sc </email> </person>

  16. Two ways of representing a DB projects: title budget managedBy employees: name ssn age

  17. Project and Employee relations in XML <db> <project> <title> Pattern recognition </title> <budget> 10000 </budget> <managedBy> Joe </managedBy> </project> <employee> <name> Joe </name> <ssn> 344556 </ssn> <age> 34 < /age> </employee> Projects and employees are intermixed <employee> <name> Sandra </name> <ssn> 2234 </ssn> <age> 35 </age> </employee> <project> <title> Auto guided vehicle </title> <budget> 70000 </budget> <managedBy> Sandra </managedBy> </project> : </db>

  18. Project and Employee relations in XML (cont’d) Employees follow projects <employees> <employee> <name> Joe </name> <ssn> 344556 </ssn> <age> 34 </age> </employee> <employee> <name> Sandra </name> <ssn> 2234 </ssn> <age>35 </age> </employee> : <employees> </db> <db> <projects> <project> <title> Pattern recognition </title> <budget> 10000 </budget> <managedBy> Joe </managedBy> </project> <project> <title> Auto guided vehicles </title> <budget> 70000 </budget> <managedBy> Sandra </managedBy> </project> : </projects>

  19. Project and Employee relations in XML (cont’d) Or without “separator” tags … <db> <projects> <title> Pattern recognition </title> <budget> 10000 </budget> <managedBy> Joe </managedBy> <title> Auto guided vehicles </title> <budget> 70000 </budget> <managedBy> Sandra </managedBy> : </projects> <employees> <name> Joe </name> <ssn> 344556 </ssn> <age> 34 </age> <name> Sandra </name> <ssn> 2234 </ssn> <age> 35 </age> : </employees> </db>

  20. Attributes An (opening) tag may contain attributes. These are typically used to describe the content of an element <entry> <wordlanguage= “en”> cheese </word> <wordlanguage= “fr”> fromage </word> <wordlanguage= “ro”> branza </word> <meaning> A food made … </meaning> </entry> Order of attributes in an element does not matter XML elements are ordered

  21. Attributes (cont’d) Another common use for attributes is to express dimension or type <picture> <height dim= “cm”> 2400 </height> <width dim= “in”> 96 </width> <data encoding = “gif”compression = “zip”> M05-.+C$@02!G96YE<FEC ... </data> </picture> A document that obeys the “nested tags” rule and does not repeat an attribute within a tag is said to be well-formed .

  22. When to use attributes It’s not always clear when to use attributes <person ssno= “123 45 6789”> <name> F. MacNiel </name> <email> fmacn@dcs.barra.ac.sc </email> ... </person> <person> <ssno>123 45 6789</ssno> <name> F. MacNiel </name> <email> fmacn@dcs.barra.ac.sc </email> ... </person>

  23. XML Misc. Apart from elements and attributes, XML allows processing instructions and comments. A processing instruction is a statement of the form: <?xmlversion="1.0"?> <?XML ENCODING="UTF-8" VERSION="1.0"?> A comment takes the following form: enclose comments between <!- - and - -> <!– - A Comment -->

  24. Document Type Descriptors Imposing structure on XML documents

  25. Document Type Descriptors • Document Type Descriptors (DTDs) impose structure on an XML document. • There is some relationship between a DTD and a schema, but it is not close -- hence the need for additional “typing” systems. • The DTD is a syntactic specification.

  26. Example: The Address Book <person> <name> MacNiel, John </name> <greet> Dr. John MacNiel </greet> <addr>1234 Huron Street </addr> <addr> Rome, OH 98765 </addr> <tel> (321) 786 2543 </tel> <fax> (321) 786 2543 </fax> <tel> (321) 786 2543 </tel> <email> jm@abc.com </email> </person> Exactly one name At most one greeting As many address lines as needed (in order) Mixed telephones and faxes As many as needed

  27. Specifying the structure • name to specify a name element • greet? to specify an optional (0 or 1) greet elements • name,greet?to specify a name followed by an optional greet

  28. Specifying the structure (cont) • addr* to specify 0 or more address lines • tel | fax a telor a fax element • (tel | fax)* 0 or more repeats of tel or fax • email* 0 or more email elements

  29. Specifying the structure (cont) So the whole structure of a person entry is specified by name, greet?, addr*, (tel | fax)*, email* This is known as a regular expression. Why is it important?

  30. Regular Expressions Each regular expression determines a corresponding finite state automaton. Let’s start with a simpler example: name, addr*, email This suggests a simple parsing program addr name email

  31. Another example name,address*,(tel | fax)*,email* address email tel tel name email fax fax email Adding in the optional greet further complicates things

  32. A DTD for the address book <!DOCTYPE addressbook [ <!ELEMENT addressbook (person*)> <!ELEMENT person (name, greet?, address*, (fax | tel)*, email*)> <!ELEMENT name (#PCDATA)> <!ELEMENT greet (#PCDATA)> <!ELEMENT address (#PCDATA)> <!ELEMENT tel (#PCDATA)> <!ELEMENT fax (#PCDATA)> <!ELEMENT email (#PCDATA)> ]>

  33. Our relational DB revisited projects: title budget managedBy employees: name ssn age

  34. Two DTDs for the relational DB <!DOCTYPE db [ <!ELEMENT db (projects,employees)> <!ELEMENT projects (project*)> <!ELEMENT employees (employee*)> <!ELEMENT project (title, budget, managedBy)> <!ELEMENT employee (name, ssn, age)> ... ]> <!DOCTYPE db [ <!ELEMENT db (project | employee)*> <!ELEMENT project (title, budget, managedBy)> <!ELEMENT employee (name, ssn, age)> ... ]>

  35. Some things are hard to specify Each employee element is to contain name, age and ssn elements in some order. <!ELEMENT employee ( (name, age, ssn) | (age, ssn, name) | (ssn, name, age) | ... )> Suppose there were many more fields !

  36. Summary of XML regular expressions • A The tag A occurs • e1,e2 The expression e1 followed by e2 • e* 0 or more occurrences of e • e? Optional -- 0 or 1 occurrences • e+ 1 or more occurrences • e1 | e2 either e1 or e2 • (e) grouping

  37. Specifying attributes in the DTD <!ELEMENT height (#PCDATA)> <!ATTLIST height dimension CDATA #REQUIRED accuracy CDATA #IMPLIED > The dimension attribute is required; the accuracy attribute is optional. CDATA is the “type” of the attribute -- it means string.

  38. The DTD Language • Default modifiers in DTD attributes:

  39. The DTD Language • Datatypes in DTD attributes:

  40. Consistency of ID and IDREF attribute values • If an attribute is declared as ID • the associated values must all be distinct (no confusion) • Id is a poor cousin of a key in relational databases. • If an attribute is declared as IDREF • the associated value must exist as the value of some ID attribute (no dangling “pointers”) • IDREF is a poor cousin of foreign key in relational databases. • Similarly for all the values of an IDREFS attribute • An attribute of type IDREFS represent a space-separated list of strings of references to valid IDs. • ID and IDREF attributes are not typed

  41. Specifying ID and IDREF attributes <!DOCTYPE family [ <!ELEMENT family (person)*> <!ELEMENT person (name)> <!ELEMENT name (#PCDATA)> <!ATTLIST person id ID #REQUIRED mother IDREF #IMPLIED father IDREF #IMPLIED children IDREFS #IMPLIED> ]>

  42. Some conforming data <family> <person id="jane" mother="mary" father="john"> <name> Jane Doe </name> </person> <person id="john" children="jane jack"> <name> John Doe </name> </person> <person id="mary" children="jane jack"> <name> Mary Doe </name> </person> <person id="jack" mother=”mary" father="john"> <name> Jack Doe </name> </person> </family>

  43. An alternative specification <!DOCTYPE family [ <!ELEMENT family (person)*> <!ELEMENT person (name, mother?, father?, children?)> <!ATTLIST person id ID #REQUIRED> <!ELEMENT name (#PCDATA)> <!ELEMENT mother EMPTY> <!ATTLIST mother idref IDREF #REQUIRED> <!ELEMENT father EMPTY> <!ATTLIST father idref IDREF #REQUIRED> <!ELEMENT children EMPTY> <!ATTLIST children idrefs IDREFS #REQUIRED> ]>

  44. The revised data <family> <person id = "jane”> <name> Jane Doe </name> <mother idref = "mary”></mother> <father idref = "john"></father> </person> <person id = "john”> <name> John Doe </name> <children idrefs = "jane jack"></children> </person> ... </family>

  45. The DTD Language • Example: Sales Order Document “An order document is comprised of several sales orders. Each individual order has a number and it contains the customer information, the date when the order was received, and the items ordered. Each customer has a number, a name, street, city, state, and ZIP code. Each item has an item number, parts information and a quantity. The parts information contains a number, a description of the product and its unit price. The numbers should be treated as attributes.”

  46. The DTD Language • Example: Sales Order Document DTD <!-- DTD for example sales order document --> <!ELEMENT Orders (SalesOrder+)> <!ELEMENT SalesOrder (Customer,OrderDate,Item+)> <!ELEMENT Customer (CustName,Street,City,State,ZIP)> <!ELEMENT OrderDate (#PCDATA)> <!ELEMENT Item (Part,Quantity)> <!ELEMENT Part (Description,Price)> <!ELEMENT CustName (#PCDATA)> <!ELEMENT Street (#PCDATA)> <!ELEMENT ... (#PCDATA)> <!ATTLIST SalesOrder SONumber CDATA #REQUIRED> <!ATTLIST Customer CustNumber CDATA #REQUIRED> <!ATTLIST Part PartNumber CDATA #REQUIRED> <!ATTLIST Item ItemNumber CDATA #REQUIRED>

  47. The DTD Language • Example: Sales Order XML Document <Orders> <SalesOrder SONumber=“12345”> <Customer CustNumber=“543”> <CustName>ABC Industries</CustName> <Street>123 Main St.</Street> <City>Chicago</City> <State>IL</State> <ZIP>60609</ZIP> </Customer> <OrderDate>10222000</OrderDate> <Item ItemNumber=“1”> <Part PartNumber=“234”> <Description>Turkey wrench</Description> <Price>9.95</Price> </Part> <Quantity>10</Quantity> </Item> </SalesOrder></Orders>

  48. A useful abbreviation When an element has empty content we can use <tag blahblahbla/> for <tag blahblahbla></tag> For example: <family> <person id = "jane”> <name> Jane Doe </name> <mother idref = "mary”/> <father idref = "john”/> </person> ... </family>

  49. Schema.dtd <!DOCTYPE db [ <!ELEMENT db (movie+, actor+)> <!ELEMENT movie (title,director,cast,budget)> <!ATTLIST movie id ID #REQUIRED> <!ELEMENT title (#PCDATA)> <!ELEMENT director (#PCDATA)> <!ELEMENT casts EMPTY> <!ATTLIST casts idrefs IDREFS #REQUIRED> <!ELEMENT budget (#PCDATA)>

  50. Schema.dtd (cont’d) <!ELEMENT actor (name, acted_In,age?, directed*)> <!ATTLIST actor id ID #REQUIRED> <!ELEMENT name (#PCDATA)> <!ELEMENT acted_In EMPTY> <!ATTLIST acted_In idrefs IDREFS #REQUIRED> <!ELEMENT age (#PCDATA)> <!ELEMENT directed (#PCDATA)> ]>

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