Introduction to XML. Leonidas Fegaras. CSE 6331 Leonidas Fegaras XML 1

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1 Introduction to XML Leonidas Fegaras CSE 6331 Leonidas Fegaras XML 1

2 Traditional DB Applications Typically business oriented Large amount of data Data is well structured, normalized, with predefined schema Large number of concurrent users (transactions) Simple data, simple queries, and simple updates Typically update intensive Small transactions High performance, high availability, scalability Data integrity and security are of major importance Good administrative support, nice GUIs CSE 6331 Leonidas Fegaras XML 2

3 Document Applications Human friendly: what you see is what you get paradigm Focus on presentation Information is divided into multiple small documents Mostly static Implicit structure: section, subsection, paragraph, etc Meta data: title, author, date, indexing keywords, etc Content structure: form/layout, inter relationships, references Tagging: eg, <p> for new paragraph Operations: retrieving, editing, spell checking, printing, etc Information retrieval: keyword queries most successful in web search engines (eg, Google) CSE 6331 Leonidas Fegaras XML 3

4 Internet Applications Challenges: Use heterogeneous, complex, hierarchical, fast evolving, unstructured/semistructured data Access mostly read only data Need 100% availability Manage millions of users world wide Have high performance requirements Are concerned with security (encryption) Like to customize data in a personalized manner Expect to gain user s trust for business to consumer transactions. Internet users choose speed and availability over correctness CSE 6331 Leonidas Fegaras XML 4

5 Electronic Commerce Currently, mostly business to business (B2B) rather than business to consumer (B2C) interactions Focus on selling and buying: Order management Product catalogs Product configuration Sales and marketing Education and training Service Communities CSE 6331 Leonidas Fegaras XML 5

6 Other Web Applications Web integration Heterogeneous data sources and types Thousands of web accessible data sources Dynamic data Data warehouses Web publishing Access different types of content from browsers (eg, , PDF, HTML, XML) Structured, dynamic, customized/personalized content Integration with application Accessible via major gateways and search engines Application integration Transformation between different application data formats (eg, XML, HTML) Integration of multiple applications CSE 6331 Leonidas Fegaras XML 6

7 Current Internet Application Architectures Architecture: Server Tier: relational databases and gateways to diverse data sources, such as, files, OLE/DB etc. Use of enterprise servers Middle Tier: provides data integration & distribution, query, etc. Consists of a web server and an application server Client Tier: mostly a web browser, may use CGI scripts or Java Characteristics: Customization is achieved at the server site (customer data in a database) with some data at the client site (cookies) Load balancing is typically hardware based (multiple servers, DNS routers) CSE 6331 Leonidas Fegaras XML 7

8 HTML opening tag closing tag <html> </html> <head><title>my Web Page</title></head> <body> <h1>introduction</h1> Look at <a href= >this document</a> <img src= image.jpg width=100 height=50> </body> attribute name hypertext link attribute value It is very simple: human readable, can be edited by any editor It reflects document presentation, not the semantics or structure of data Universal: portable to any platform HTML pages are connected through hypertext links HTML pages can be located using web search engines CSE 6331 Leonidas Fegaras XML 8

9 XML XML (extensible Markup Language) is a textual language for representing and exchanging data on the web. It is designed to improve the functionality of the Web by providing more flexible and adaptable information identification Based on SGML and was developed around 1996 It is called extensible because it is not a fixed format like HTML (a single, predefined markup language). Instead, XML is actually a metalanguage a language for describing other languages which lets you design your own customized markup languages for limitless different types of documents XML can be untyped (semistructured), but there are standards now for schema conformance (DTD and XML Schema) Without schema, an XML document is well formed if it satisfies simple syntactic constraints: proper nesting of start and end tags CSE 6331 Leonidas Fegaras XML 9

10 Example <people> <person> <name> Leonidas Fegaras </name> <tel> (817) </tel> < > </ > </person> <person> <name> Ramez Elmasri </name> <tel> (817) </tel> < > </ > </person> </people> CSE 6331 Leonidas Fegaras XML 10

11 Why XML is so Popular? It looks like HTML simple, human readable, easy to learn, universal Flexible & extensible, since you can represent any kind of data unlike HTML HTML describes the presentation while XML describes the content Precise well formed: properly nested XML tags valid: its structure may conform to a DTD or an XML Schema Supported by the W3C trusted and adopted by industry Many standards around XML: schemas, query languages, etc CSE 6331 Leonidas Fegaras XML 11

12 What XML has to do with Databases? XML is an important standardization for data representation and exchange, but still needs to store and query large repositories of XML documents data models and schema representations query languages, data indexing, query optimizers updates, view maintenance concurrency, distribution, security, etc Example application: an XML data repository distributed in a peer to peer network answer queries, such as: find all books whose author is Smith and whose title contains the word XML much like a web search engine, but for XML,... and for more precise querying CSE 6331 Leonidas Fegaras XML 12

13 XML Syntax XML consists of tags and text XML documents conform to the following grammar: XMLdocument ::= Pi* Element Pi* Element ::= Stag (char Pi Element)* Etag Stag ::= '<'Name Atts '> Etag ::= '</'Name '> Pi ::= '<?'char* '?> Atts ::= ( Name '='String )* String ::= '"'char* '" Tags come in pairs <date>8/25/2004</date> and must be properly nested: <person> <name>... </name>... </person> valid nesting <person> <name>... </person>... </name> invalid nesting Text is bounded by tags. PCDATA: parsed character data. eg, <title> The Big Sleep </title> <year> 1935 </ year> CSE 6331 Leonidas Fegaras XML 13

14 XML Elements An element is a segment of an XML document between an opening and the matching closing tags <person> <name> Ramez Elmasri </name> <tel> (817) </tel> < > elmasri@cse.uta.edu </ > </person> An element may contain a mixture of sub elements and PCDATA <title>an <em>element</em> is a segment</title> An abbreviation: for an element with empty content, we can use: <tagname... /> instead of: <tagname...></tagname> CSE 6331 Leonidas Fegaras XML 14

15 Representing Data Using XML Nesting tags can be used to express various structures, such as a record: <person> <name> Ramez Elmasri </name> <tel> (817) </tel> < > elmasri@cse.uta.edu </ > </person> We can represent a list by using the same tag repeatedly: <addresses> <person>... </person> <person>... </person> <person>... </person>... </addresses> CSE 6331 Leonidas Fegaras XML 15

16 XML structure XML: is Lisp like: <person> </person> (person (name Ramez Elmasri ) <name> Ramez Elmasri </name> <tel> (817) </tel> < > elmasri@cse.uta.edu </ > (tel (817) ) ( elmasri@cse.uta.edu )) and tree like: person name tel Ramez Elmasri (817) elmasri@cse.uta.edu CSE 6331 Leonidas Fegaras XML 16

17 Attributes An opening tag may contain attributes typically used to describe the content of an element <author ssn=" "> <name>ramez Elmasri</name> < > </ > </author> It's not always clear when to use attributes <author> <ssn> </ssn> <name>ramez Elmasri</name> < > </ > </author> ID attributes are special: must be unique within the document An IDref attribute must refer to an existing ID in the same doc CSE 6331 Leonidas Fegaras XML 17

18 Referencing Elements Using IDs/IDrefs <family> <person id="jane" mother="mary" father="john"> <name> Jane Doe </name> </person> <person id="john" children="jane jack"> <name> John Doe </name> <mother/> </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> CSE 6331 Leonidas Fegaras XML 18

19 A Complete Example <?xml version="1.0"?> <!DOCTYPE bib SYSTEM "bib.dtd"> <bib> <vendor id="id0_1"> <name>amazon</name> <phone> </phone> <book> <title>unix Network Programming</title> <publisher>addison Wesley</publisher> <year>1995</year> <author> <firstname>richard</firstname> <lastname>stevens</lastname> </author> <price>38.68</price> </book> <book> <title>an Introduction to Object Oriented Design</title> <publisher>addison Wesley</publisher> <year>1996</year> <author> <firstname>jo</firstname> <lastname>levin</lastname> </author> <author> <firstname>harold</firstname> <lastname>perry</lastname> </author> <price>11.55</price> </book> </vendor> </bib> CSE 6331 Leonidas Fegaras XML 19

20 OODB Schema class Movie ( extent Movies, key title ) { attribute string title; attribute string director; relationship set<actor> casts inverse Actor::acted_In; attribute int budget; } ; class Actor ( extent Actors, key name ) { attribute string name; relationship set<movie> acted_in inverse Movie::casts; attribute int age; attribute set<string> directed; } ; CSE 6331 Leonidas Fegaras XML 20

21 In XML <db> <movie id= m1 > <title>waking Ned Divine</title> <director>kirk Jones III</director> <cast idrefs= a1 a3 ></cast> <budget>100,000</budget> </movie> <movie id= m2 > <title>dragonheart</title> <director>rob Cohen</director> <cast idrefs= a2 a9 a21 ></cast> <budget>110,000</budget> </movie> <movie id= m3 > <title>moondance</title> <director>dagmar Hirtz</director> <cast idrefs= a1 a8 ></cast> <budget>90,000</budget> </movie> <actor id= a1 > <name>david Kelly</name> <acted_in idrefs= m1 m3 m78 > </acted_in> </actor> <actor id= a2 > <name>sean Connery</name> <acted_in idrefs= m2 m9 m11 > </acted_in> <age>68</age> </actor> <actor id= a3 > <name>ian Bannen</name> <acted_in idrefs= m1 m35 > </acted_in> </actor> : </db> CSE 6331 Leonidas Fegaras XML 21

22 DTD: Document Type Descriptor A DTD imposes a structure on an XML document Not quite a typing system it is purely syntactic now replaced by XML Schema Uses regular expressions to specify structure firstname an element with tag name firstname book* zero or more books year? an optional year firstname,lastname a firstname followed by lastname book journal either a book or a journal CSE 6331 Leonidas Fegaras XML 22

23 Example of XML Data <bib> <vendor id="id0_1"> <name>amazon</name> <phone> </phone> <book> <title>unix Network Programming</title> <publisher>addison Wesley</publisher> <year>1995</year> <author> <firstname>richard</firstname> <lastname>stevens</lastname> </author> <price>38.68</price> </book>... </vendor> </bib> CSE 6331 Leonidas Fegaras XML 23

24 DTD Example <?xml encoding="iso "?> <!ELEMENT bib (vendor)*> <!ELEMENT vendor (name, , book*)> <!ATTLIST vendor id ID #REQUIRED> <!ELEMENT book (title, publisher?, year?, author+, price)> <!ELEMENT author (firstname?, lastname)> <!ELEMENT name (#PCDATA)> <!ELEMENT (#PCDATA)> <!ELEMENT title (#PCDATA)> <!ELEMENT publisher (#PCDATA)> <!ELEMENT year (#PCDATA)> <!ELEMENT firstname (#PCDATA)> <!ELEMENT lastname (#PCDATA)> <!ELEMENT price (#PCDATA)> CSE 6331 Leonidas Fegaras XML 24

25 Summary of the DTD Syntax A tagged element in a DTD is defined by <!ELEMENT name e> where e is a DTD expression If e, e1, e2 are DTD expressions, then so are: EMPTY empty content #PCDATA any text A an element with tag name A e1,e2 e1 followed by e2 e1 e2 either e1 or e2 e* zero or more occurrences of e e+ one or more occurrences of e e? optional e (zero or one occurrences) (e) Note: tagged elements are global must be defined once in a DTD CSE 6331 Leonidas Fegaras XML 25

26 DTD Syntax (cont.) Attribute specification: <!ATTLIST name (attribute name type accuracy?)+> type is: ID must be unique within the document IDREF a reference to an existing ID IDREFS multiple IDREFs CDATA any string accuracy is #REQUIRED, #IMPLIED, #FIXED 'value', value 'v1... vn' ID, IDref, and IDrefs attributes are not typed! Example: <!ELEMENT person (#PCDATA)> <!ATTLIST person id ID #REQUIRED children IDrefs #IMPLIED > the id attribute is required while the children attribute is optional CSE 6331 Leonidas Fegaras XML 26

27 Connecting an XML document to a DTD In line the DTD into the XML file: <?xml version= 1.0?> <!DOCTYPE db [ <!ELEMENT person...>... ]> <db> <person>... </person>... </db> DTD XML data Better: put the DTD in a separate file and reference it by URL: <!DOCTYPE db SYSTEM > Documents are validated against their DTD before they are used CSE 6331 Leonidas Fegaras XML 27

28 Recursive DTDs We want to capture a person with a mother and a father First attempt: <!ELEMENT person (name, address, person, person)> where the first person is the mother while the second is the father Second attempt: <!ELEMENT person (name, address, person?, person?)> Third attempt: <!ELEMENT person (name, address)> <!ATTLIST person id ID #REQUIRED mother IDREF #IMPLIED father IDREF #IMPLIED> CSE 6331 Leonidas Fegaras XML 28

29 Back to the OODB Schema class Movie ( extent Movies, key title ) { attribute string title; attribute string director; relationship set<actor> casts inverse Actor::acted_In; attribute int budget; } ; class Actor ( extent Actors, key name ) { attribute string name; relationship set<movie> acted_in inverse Movie::casts; attribute int age; attribute set<string> directed; } ; CSE 6331 Leonidas Fegaras XML 29

30 DTD <!ELEMENT db (movie+, actor+)> <!ELEMENT movie (title, director, cast, budget)> <!ATTLIST movie id ID #REQUIRED> <!ELEMENT title (#PCDATA)> <!ELEMENT director (#PCDATA)> <!ELEMENT cast EMPTY> <!ATTLIST cast IDREFS #REQUIRED> <!ELEMENT budget (#PCDATA)> <!ELEMENT actor (name, acted_in, age, directed*)> <!ELEMENT name (#PCDATA)> <!ELEMENT acted_in EMPTY> <!ATTLIST acted_in IDREFS #REQUIRED> <!ELEMENT age (#PCDATA)> <!ELEMENT directed (#PCDATA)> CSE 6331 Leonidas Fegaras XML 30

31 XML Namespaces When merging multiple docs together, name collisions may occur A namespace is a mechanism for uniquely naming tagnames and attribute names to avoid name conflicts Tag/attribute names are now qualified names (QNames) (namespace ':')? localname example: bib:author A document may use multiple namespaces A DTD has its own namespace in which all names are unique A namespace in an XML doc is defined as an attribute: xmlns:bib= where bib is the namespace name and the URL is the location of the DTD The default namespace is defined as xmlns= URL If not defined, it is the global namespace CSE 6331 Leonidas Fegaras XML 31

32 Example <item xmlns= xmlns:toy= > <name>backpack</name> <feature> <toy:item> <toy:name>cyberpet</toy:name> </toy:item> </feature> </item> CSE 6331 Leonidas Fegaras XML 32

33 Query Languages for XML Need a language for XML data for extracting fragments (querying) restructuring (data transformation) integrating (eg, combining multiple XML documents) browsing presentation (eg, from XML to HTML) We will first learn XPath used in extracting fragments from a single document many XML query languages are based on XPath We will briefly discuss XSLT for extracting, restructuring, and presentation over a single document We will focus later on XQuery a full fledged query language much like OQL CSE 6331 Leonidas Fegaras XML 33

34 XPath Describes a single navigation path in an XML document Selects a sequence of nodes reachable by the path the order of nodes is the document order Main construct: axis navigation Consists of one or more navigation steps separated by / A navigation step is a triplet axis :: node test list of predicates Each navigation path is evaluated relative to a context node Examples: /child::bib /descendant::author /descendant::book [ /child::author = Smith ] /child::title Most people use shorthands /bib//author //book[author= Smith ]/title CSE 6331 Leonidas Fegaras XML 34

35 Axis Navigation In the beginning, the context node is the document root Dot (.) identifies the context node Some navigation steps: / the root node // the root node and its descendants./author all the children of the context node with tagname author; the context node of the next step is each of these children.// the context node and all its descendants; the context node of the next step is each of the the attribute value of the attribute name mother of the context node./* all the children of the context node.. parent of context node text() all the text children of the context node Shortcut: you can remove./ CSE 6331 Leonidas Fegaras XML 35

36 Example <a> <b> <c></c> <b></b> </b> <d> <c></c> </d> <b> <d></d> </b> </a> c b b 1 a d b c d /./a or /a > [1] /./a./b or /a/b > [2,4] /a/c > [] /a/*/c > [5,7] //b > [2,6,4] //b/c > [5] /a//c > [5,7] CSE 6331 Leonidas Fegaras XML 36

37 Predicates Many variations [10] the tenth child node of the context node [last()] the last child node of the context node [author] true, if the context node has at least one child tagged author [author/name] true, if the XPath./author/name is nonempty author[name= Smith ] true if the author name is Smith Examples /bib/book[@price < 100 ]/title /bib/book[author/text()] author[name/firstname= Smith and name/lastname= John ]/title /bib/book/author[name/firstname][address[//zip][city]]/name/lastname CSE 6331 Leonidas Fegaras XML 37

Introduction. Leonidas Fegaras University of Texas at Arlington. Web Data Management and XML L1: Introduction 1

Introduction. Leonidas Fegaras University of Texas at Arlington. Web Data Management and XML L1: Introduction 1 Introduction Leonidas Fegaras University of Texas at Arlington Web Data Management and XML L1: Introduction 1 Information Class: TuTh 2:00-3:20pm (NH 111) Instructor: Leonidas Fegaras Office: GACB 115