Maziar Sanaii Ashtiani – SCT – EMU, Fall 2011/12

 HTTP  Standard Generalized Markup Language  eXtensible Markup Language ▪ Useful as a data format to exchange between apps ▪ Markup means something not mentioned in the document ▪ Has tags enclosed n angle brackets ▪ Database Systems Concepts

Comp. Sci. Taylor CS-101 Intro. to Computer Science Comp. Sci Srinivasan Comp. Sci CS-101

 Tags are self documenting  No rigid format  Can evolve over time  Nested structures  Widely accepted  Lots of tools XML has become THE dominant format for data exchange

 Elements  Single root  Proper nesting   Text in the context of an element  May be mixed with subelements  Nesting to avoid joins (fig. 23.5, 23.6)

 Attributes  name= value  Strings  Useful as identifiers  Namespace   Literal values  · · · ]]>

 Databases have schemas  XML  Document Type Definition  XML Schema  Relax NG

<!DOCTYPE university [ ] >

<!DOCTYPE university-3 [ <!ATTLIST department dept_name ID #REQUIRED > <!ATTLIST course course_id ID #REQUIRED dept_name IDREF #REQUIRED instructors IDREFS #IMPLIED > dept name IDREF #REQUIRED > · · · declarations for title, credits, building,budget, name and salary · · · ] >

 No constraints  Data verification needed  No limit over occurrence  Lack of typing for ID and IDREF

 Result of deficiencies in DTD  Has string, integer, decimal,…  User defined types

<xs:element ref=“department” minOccurs=“0” maxOccurs=“unbounded”/> <xs:element ref=“course” minOccurs=“0” maxOccurs=“unbounded”/> <xs:element ref=“instructor” minOccurs=“0” maxOccurs=“unbounded”/> <xs:element ref=“teaches” minOccurs=“0” maxOccurs=“unbounded”/> 

 PK  FK

 Constraints  User-defined types  PK and FK  Integrated namespaces  Min and Max values  Type extension by inheritence

 XPath  Language for path expressions  XQuery  Standard language for querying XML ▪ Modeled after SQL but different ▪ Deal with nested XML data

 Trees and nodes  Elements and attributes  XPath 2.0  /university-3/instructor/name ▪ Srinivasan ▪ Brandt

 Selection  /university-3/course[credits >= id  Functions  Count() ▪ /university-2/instructor[count(./teaches/course)> 2]  id(“foo”)  Union “|”  …

 W3C  XQuery 1.0 ▪ For ▪ Let ▪ Where ▪ Order by ▪ Return

for $x in /university-3/course let $courseId := where $x/credits > 3 return { $courseId } is equivalent to for $x in /university-3/course[credits > 3] return { id }

for $c in /university/course, $i in /university/instructor, $t in /university/teaches where $c/course_id= $t/course id and $t/IID = $i/IID return { $c $i } which is equivalent to for $c in /university/course, $i in /university/instructor, $t in /university/teaches[ $c/course id= $t/course id and $t/IID = $i/IID] return { $c $i }

declare function local:dept_courses($iid as xs:string) as element(course)* { for $i in /university/instructor[IID = $iid], $c in /university/courses[dept name = $i/dept_name] return $c }

 Document Object Model  JAVA DOM API  Simple API for XML  Event model

 Non-relational Data Stores  Flat files (NO ACID)  XML Database ▪ DOM C++-based

 Relational Databases  Store as string ▪ clob  Tree Representation  Map to Relations  Publishing and Shredding XML Data  Native Storage within Relational Database

select xmlelement (name “course”, xmlattributes (course id as course id, dept name as dept name), xmlelement (name “title”, title), xmlelement (name “credits”, credits)) from course

 Storing Data With Complex Structure  ODF  OOXML  Standardized Data Exchange Format  B2B  Web Services – HTTP  SOAP  WSDL  Data Mediation – Wrappers