XML and Web Services

Transcription

1 XML and Web Services Lecture 8 1 XML (Section 17) Outline XML syntax, semistructured data Document Type Definitions (DTDs) XML Schema Introduction to XML based Web Services 2

2 Additional Readings on XML XML (1/99) Main source: (but hard to read) Several XML tutorials on the Web 3 XML extensible Markup Language XML 1.0 a recommendation from W3C, 1998 Roots: SGML (used in publishing). Standardized General Markup Language After the roots: a format for sharing data 4

3 XML Data Relational data does not have a syntax I can!t give you my relational database Need to import it from other syntax, like CSV (comma-separated-values) XML = rich syntax for data But XML is not relational: semi-structured Usage: Map any data to XML Store it in files, exchange on the Web, Web services etc. Even query it directly, using XPath, XQuery 5 XML Data Sharing and Exchange application object-relational application XML Data Integrate WEB (HTTP) Transform Warehouse relational data application legacy data Specific data management tasks 6

4 From HTML to XML HTML describes the layout 7 HTML <h1> Bibliography </h1> <p> <i> Foundations of Databases </i> Abiteboul, Hull, Vianu <br> Addison Wesley, 1995 <p> <i> Data on the Web </i> Abiteoul, Buneman, Suciu <br> Morgan Kaufmann,

5 <bibliography> <book> </book> </bibliography> XML <title> Foundations </title> <author> Abiteboul </author> <author> Hull </author> <author> Vianu </author> <publisher> Addison Wesley </publisher> <year> 1995 </year> XML describes the structure 9 XML Terminology tags: book, title, author, start tag: <book>, end tag: </book> elements: <book> </book>,<author> </author> elements are nested empty element: <red></red> abbrv. <red/> well formed XML document if it has matching tags tags are properly nested single root element and more constraints, e.g. on names 10

6 More XML: Attributes <book price = 55 currency = EUR > <title> Foundations of Databases </title> <author> Abiteboul </author> <year> 1995 </year> </book> attributes are alternative ways to represent data 11 XML example <?xml version='1.0' encoding='utf-8'?> <!-- A full XML Example --> <book price = 55 currency = EUR > <title> Foundations of Databases </title> <author> Abiteboul </author> <year> 1995 </year> </book> 12

7 More XML: Comments Syntax <!--... Comment text... --> Same syntax as in HTML Yes, they are part of the data model!!! Good documentation should be provided using comments In particular for Web services (see later) 13 XML Data: a Tree! <data> <person id= o555 > <name> Mary </name> <address> <street> Maple </street> <no> 345 </no> <city> Seattle </city> </address> </person> <person> <name> John </name> <address> Thailand </address> <phone> </phone> </person> </data> id o555 Attribute node name Mary person address street no city data Maple 345 Seattle Order matters!!! name John person address Thai Text node Element node 14 phone 23456

8 More XML: IDs and References <person id= o555 > <name> Jane </name> </person> <person id= o456 > <name> Mary </name> </person> <children idref= o123 o555 /> <person id= o123 mother= o456 ><name>john</name> </person> Scope of IDs and references is the document 15 From Relational Data to XML Data persons XML: persons row row row Name John Sue Dick Phone name phone name phone name phone John 3634 Sue 6343 Dick 6363 <persons> <row> <name>john</name> <phone> 3634</phone></row> <row> <name>sue</name> <phone> 6343</phone> <row> <name>dick</name> <phone> 6363</phone></row> </persons> 16

9 XML Data XML is self-describing Schema elements become part of the data Relational schema: persons(name,phone) In XML <persons>, <name>, <phone> are part of the data, and are repeated many times Consequence: XML is much more flexible However, XML data is redundant! XML = semi-structured data 17 Structured / Unstructured / Semi-Structured Data Structured data Organised in semantic chunks (entities) Are grouped together, have same format Unstructured data Data can be of any type Semi-structured data Entities may not have the same attributes Not all attributes may be required Order of attributes not necessarily important Nested and heterogeneous 18

10 Semi-structured Data Explained Missing attributes: Could represent in a table with nulls <person> <name> John</name> <phone>1234</phone> </person> <person> <name>joe</name> </person>! no phone! name John Joe phone Semi-structured Data Explained Repeated attributes <person> <name> Mary</name> <phone>2345</phone> <phone>3456</phone> </person>! two phones! Impossible in tables: name Mary phone ??? 20

11 Semi-structured Data Explained Attributes with different types in different objects <person> <name> <first> John </first> <last> Smith </last> </name> <phone>1234</phone> </person>! structured name! Nested collections (no 1NF) Heterogeneous collections: <db> contains both <book>s and <publisher>s 21 How to describe data types/schema? In XML we basically have two options: Document Type Description (DTD) Since early days of XML Allows for document validation Limited support for data types XML Schema Allows for simple and complex data types Has mainly replaced DTD 22

12 Document Type Definitions DTD Part of the original XML specification an XML document may have a DTD XML document: well-formed = if tags are correctly closed valid = if it has a DTD and conforms to it Validation is useful in data exchange 23 Very Simple DTD <!DOCTYPE company [ <!ELEMENT company ((person product)*)> <!ELEMENT person (ssn, name, office, phone?)> <!ELEMENT ssn (#PCDATA)> <!ELEMENT name (#PCDATA)> <!ELEMENT office (#PCDATA)> <!ELEMENT phone (#PCDATA)> <!ELEMENT product (pid, name, description?)> <!ELEMENT pid (#PCDATA)> <!ELEMENT description (#PCDATA)> ]> 24

13 Very Simple DTD Example of valid XML document: <company> <person> <ssn> </ssn> <name> John </name> <office> B432 </office> <phone> 1234 </phone> </person> <person> <ssn> </ssn> <name> Jim </name> <office> B123 </office> </person> <product>... </product>... </company> 25 DTD: The Content Model <!ELEMENT tag (CONTENT)> Content model: content model Complex = a regular expression over other elements Text-only = #PCDATA Empty = EMPTY Any = ANY Mixed content = (#PCDATA A B C)* * 0 or many + at least one? 0 or 1 26

14 DTD: Regular Expressions sequence DTD <!ELEMENT name (firstname, lastname)) optional <!ELEMENT name (firstname?, lastname)) star (repeated occurrence) <!ELEMENT person (name, phone*)) alternation <!ELEMENT person (name, (phone ))) XML <name> <firstname>..... </firstname> <lastname>..... </lastname> </name> <name> <lastname>..... </lastname> </name> <person> <name>..... </name> <phone>..... </phone> <phone>..... </phone> <phone>..... </phone> </person> <person> <name>..... </name> < >..... </ > 27 </person> DTD: Attributes Document Type Definition <!ELEMENT person (ssn, name, office, phone?)> <!ATTLIST person age CDATA #REQUIRED "18" birthdate CDATA #IMPLIED nationality CDATA #FIXED "CH" gender (male female) "female"> Document <person age="24" nationality="ch" gender="male"> <ssn> </ssn> <phone> </phone> </person> mandatory optional default enumeration 28

15 Inclusion of DTD in Documents External DTD Declaration <?xml version="1.0" encoding="iso "?> <!DOCTYPE test PUBLIC "-//Test AG//DTD test V1.0//EN" SYSTEM " <test> "test" is a document element </test> Internal DTD Declaration <!DOCTYPE test [ <!ELEMENT test EMPTY> ]> <test/> Mixed usage <!DOCTYPE test SYSTEM " [ <!ENTITY hello "hello world"> ]> <test>&hello;</test> 29 XML Schema DTD has restrictions Only allows for very simple data types XML Schema Uses same syntax as XML documents Allows for basic (built-in) and complex data types integer, float, boolean, string etc. 30

16 XML Schema Example <element name= Person type= string /> <element name= age type= integer /> <Person>Antonia</Person> <age>23</age> Would like to have an entity called Person 31 Complex Types <complextype name= Person > <sequence> <element name= Name type= string > <element name= age type= integer > <element name= Address type= string minoccurs= 1 maxoccurs= unbounded > </sequence> </complextype> <Person> <Name>Antonia</Name> <age>23</age> <Address>1015 Lausanne</Address> <Address>1010 Vienna</Address> </Person> 32

17 XML Namespaces Different DTDs/XMLSchemas can use the same names! how to avoid conflicts when combining names from different DTDs/XMLSchemas? XML namespace is a collection of names (markup vocabulary) identified by a prefix (URL reference) 33 XML Namespaces name ::= [prefix:]localname <book xmlns='urn:loc.gov:book' xmlns:isbn=' <title> </title> <number> 15 </number> <isbn:number>. </isbn:number> </book> default name space names belong to default name space 34

18 XML Namespaces syntactic: <number>, <isbn:number> semantic: URL used as unique identifier URL may not exist, has no function <tag xmlns:mystyle = > Belong to this namespace <mystyle:title> </mystyle:title> <mystyle:number> </tag> 35 <?xml version="1.0" encoding="iso "?> <xs:schema xmlns:xs=" <xs:element name="shiporder"> <xs:complextype> <xs:sequence> <xs:element name="orderperson" type="xs:string"/> <xs:element name="shipto"> <xs:complextype> <xs:sequence> <xs:element name="name" type="xs:string"/> <xs:element name="address" type="xs:string"/> <xs:element name="city" type="xs:string"/> <xs:element name="country" type="xs:string"/> </xs:sequence> </xs:complextype> </xs:element> <xs:element name="item" maxoccurs="unbounded"> <xs:complextype> <xs:sequence> <xs:element name="title" type="xs:string"/> <xs:element name="note" type="xs:string" minoccurs="0"/> <xs:element name="quantity" type="xs:positiveinteger"/> <xs:element name="price" type="xs:decimal"/> </xs:sequence> </xs:complextype> </xs:element> </xs:sequence> <xs:attribute name="orderid" type="xs:string" use="required"/> </xs:complextype> </xs:element> </xs:schema> 36

19 XML (Section 17) Outline XML syntax, semistructured data Document Type Definitions (DTDs) XML Schema Introduction to XML based Web Services 37 What is a Web Service? A Web service is a network accessible interface to application programs, built using standard Internet technologies. Clients of Web services do NOT need to know how it is implemented. Application client Network Web Service Application program 38

20 Web Server vs. Web Service Web Server Typically an HTTP server that serves Web pages such as the EPFL Web site Web Service Provides a programmable interface to client applications Typically uses SOAP for communication We can write Java, C++,, applications to access the service 39 Web Services: Some Definitions A Web Service is a URL-addressable software resource that performs functions (or a function). "Web services are a new breed of Web application. They are self-contained, self-describing, modular applications that can be published, located, and invoked across the Web. Web services perform functions, which can be anything from simple requests to complicated business processes. Once a Web service is deployed, other applications (and other Web services) can discover and invoke the deployed service. IBM web service tutorial 40

21 Let!s work out the details Client and server need to speak a certain protocol HTTP, home-grown, SOAP, etc. Messages need to be exchanged between client and server Communication should be fast Independent of programming language, operating system etc. 41 Example: InfoPoint Service Assume a service that returns temperature, time etc. of a certain city: client San Francisco, time 0:30 PST San Francisco, temp 11 C InfoPoint Service 42

22 Messages, Remote Procedures Client should have the impression to call a (remote) procedure Should be able to do that from her programming language String gettime(string city) String gettemp(string city) int getaltitude(string city) 43 How do we exchange data/messages? Server needs to Listen on a certain port Speak a certain protocol Example (in class): Open a socket connection and use TCP/IP Send a few bytes Write data to the network Wait for a response Read data from network What is the problem with home-grown protocols on top of TCP/IP? 44

23 HTTP (Hyper Text Transfer Protocol) Standardised way of exchanging requests and responses Mainly design for exchange of Web pages or data Response Request GET /index.html HTTP/1.1 Host: server.example.org HTTP/ OK Connection: close Content-Length: 80 Content-Type: text/html Date: Wed, 25 Feb :07:42 GMT <HTML> <BODY> <H1>Introduction to Info Sys</H1> The course provides </BODY> 45 </HTML> Request Example: InfoPoint Service How do we tell the service: Which method to call? Which parameters (data types)? POST /InfoPoint HTTP/1.1 Host: server.example.org gettime( San Francisco ) HTTP/ OK Connection: close Content-Length: 80 Content-Type: text/html Date: Wed, 25 Feb :07:42 GMT Time=0:30 Response 46

24 XML for Message Exchange Requests and responses can be translated into XML Use data types such as defined in XML Schema Provides a powerful way to map methods into requests/responses This is the main idea of SOAP based Web Services 47 InfoPoint in XML String gettime(string city) String gettemp(string city) int getaltitude(string city) Request Response <InfoPoint> <gettimerequest> <city>san Francisco</city> </gettimerequest> </InfoPoint> <InfoPoint> <gettimeresponse> <time>0:30 PST</time> </gettimeresponse> </InfoPoint> 48

25 Putting it all together: XML over HTTP Send XML file with HTTP Request Receive XML file in HTTP Response Request POST /InfoPoint HTTP/1.1 Host: server.example.org <InfoPoint> <gettimerequest> <city>san Francisco</city> </gettimerequest> </InfoPoint> Response HTTP/ OK Connection: close Content-Type: text/xml Date: Wed, 25 Feb :07:42 GM <InfoPoint> <gettimeresponse> <time>0:30 PST</time> </gettimeresponse> </InfoPoint> 49 Web Service Architecture "server" Service provider publish (WSDL) bind (SOAP) Service broker "naming service" find (UDDI) Service requestor "client" 50

26 Advantages of Web Services Platform independence Not bound to any programming language nor operating system Client only needs to understand HTTP (TCP/IP) XML A standardised protocol exists to create XML requests/responses: SOAP Will be discussed next time In principle, simple to understand, implement 51 Disadvantages of Web Services XML data is exchanged: Often, lots of redundancy in messages Can lead to performance issues Not designed for high-performance data exchange 52

27 Outlook: Web Service Implementations Often provided on top of existing HTTP based Web servers or application servers Stand-alone Web service containers Axis for Java SOAP HTTP Web Server client 53 Summary XML provides a powerful means for semi-structured data exchange Relational tables can easily be exported into XML Web Services Use XML to exchange messages 54