XML 101 A Technical Introduction to XML 20

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XML 101: A Technical Introduction to XML 20 November 2002 Bank of Montreal Database Users Group Ian GRAHAM IT Strategy, IBS, Technology and Solutions, BMO Financial Group E: T: (416) 513. 5656 / F: (416) 513. 5590 To download this talk: http: //www. utoronto. ca/ian/talks/ IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 1

Presentation Outline 1. What is XML (basic introduction) 2. Defining language dialects and constraints – DTDs, namespaces, and schemas 3. XML processing – Parsers and parser interfaces; XML processing tools 4. XML databases – High-level issues, and references 5. XML messaging / web services – Why, and some issues/example 6. Conclusions IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 2

What is XML? · A base-level syntax – for encoding structured, text-based information (words, characters, . . . ) · A text-based syntax – XML is written using printable Unicode characters. Explicit binary data is not allowed · Supports extensible data formats – XML lets you define your own elements (essentially data types), within the constraints of the syntax rules · Designed as a universal format – The syntax rules ensure that all XML processing software MUST identically handle a given piece of XML data. If you can read and process it, so can anybody else IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 3

XML: A Simple Example XML Declaration (“this is XML”) Flags character encoding used in file Gold sprockel grommets, with matching hamster 12 . . . Order something else. . . Black – XML tags and markup Blue - encoded text data IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 4

Example Revisited element tags attribute of this quantity element Gold sprockel grommets, with matching hamster 12 . . . Order something else. . . Hierarchical, structured data IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 5

XML Data Model - A Tree ref= date= . . text. .

XML: Design goals · Simple but reliable – Strict syntax rules, to eliminate syntax errors – syntax defines structure (hierarchically), and names structural parts (element names) -- it is self-describing data · Extensible and ‘mixable’ – Can create your own language of tags/elements – Can mix one language with another, and still reliably separate / process the data · Designed for a distributed environment – Can have remote (‘webbed’) data, and retrieve and use it reliably IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 7

XML Processing: The XML Parser parser Interface XML data XML parser XML-based application · The parser must verify that the XML is syntactically correct · Such data is said to be well-formed – The minimal requirement to “be” XML · A parser MUST stop processing if the data isn’t well-formed – E. g. , stop processing and “throw an exception” to the XML-based application. The XML 1. 0 spec requires this behaviour IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 8

Special Issues: Characters and Charsets · XML specification defines characters allowed as whitespace in tags: · You cannot use EBCIDIC character ‘NEL’ as whitespace – Must make sure to not do so! · What if you want to include characters not defined in the encoding charset (e. g. , Greek characters in an ISO-Latin-1 document): – Use character references. For example: ♠ -- the spades character ( ) 9824 th character in the Unicode character set · Also, a reminder that binary data is forbidden – must be encoded as printable characters (e. g. using Base 64) IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 9

Parsers and DTDs parser interface XML data parser XML-based application DTD – A DTD can define external parts (entities) to be ‘included’ in – But …. what if the parser can’t find the external parts (firewall? )? – That depends on the type: there are two types of XML parsers • one that MUST retrieve all parts • one that can ignore them (if it can’t find them) IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 10

Two types of XML parsers · Validating – Must retrieve all entities and process all of the DTD. Will stop processing and indicate a failure if it cannot – It must also test and verify other things in the DTD -- instructions that define syntactic document rules (allowed elements, attributes, etc. ). · Non-validating (well-formed only) – Tries retrieve all ‘parts’, but will cease processing the DTD content at the first part (entity) it can’t find, – But this is not an error -- the parser simply makes available the XML data (and the names of any unresolved ‘parts’) to the application. Application behavior will depend on parser type Many parsers can operate in either mode (config) IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 11

Defining constraints / languages · Two ways of doing so: – XML Document Type Declaration (DTD) -- Part of core XML spec. – XML Schema (often called XSD) -- New specification (2001), which allows for richer constraints on XML documents. · What DTDs and/or schema specify: – Allowed element and attribute names, hierarchical nesting rules; element content/type restrictions · Adding dialect specifications implies two classes of XML data – Well-formed – Valid XML that is syntactically correct XML that is well-formed and consistent with a specific DTD (or Schema) · Schemas are more powerful than DTDs – Often used for type validation, or for defining low-level type constraints (integer, varchar, datetime, etc. ) constraints on values. IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 13

DTD Example <!DOCTYPE transfers [ <!ELEMENT transfers (funds. Transfer)+ > <!ELEMENT funds. Transfer (from, DTD Example . . . Omitted DTD content. . . ]> . . . As with previous example. . . IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 14

XML Namespaces · Mechanism for identifying different “spaces” for XML names – That is, element or attribute names · This is a way of identifying different language dialects, consisting of names that have specific semantic (and processing) meanings. · For example in one language (e. g. a security key) can be distinguised from in another language (a database key) · Mechanism uses a special xmlns attribute to define namespaces. – The namespace is a URL string – But the URL does not reference anything in particular (there may be nothing there!) IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 15

Mixing languages together Namespaces let you do this relatively easily: Default ‘space’ is xhtml Heading of Page . . . Math. ML markup. . . mt: prefix indicates

more html stuff goes here

‘space’ mathml (a

different language) IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 16

XML Schemas · A specification for defining XML validation rules Specs: Best-practice: http: //www. w 3. org/XML/Schema http: //www. xfront. com/Best. Practices. Homepage. html · Uses pure XML (plus namespaces) to do this · More powerful than DTDs - can specify things like integer types, date strings, real numbers in a given range, etc. · Often used for type validation, or for relating database schemas to XML models · They don’t, however, let you declare entities -- those can only be done in DTDs · The following slide shows the XML schema equivalent to our DTD IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 17

XML Schema version of our DTD (Portion) . . . (some stuff omitted). . . . . . And still more !!!. . . IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 18

XML Software · XML parsers…. . – Read in XML data, checks for syntactic (and possibly DTD/Schema) constraints, and makes data available to an application. There are three 'generic' parser APIs • • SAX DOM JDOM Pull Simple API to XML Document Object Model Java Document Object Model evolving API (new) (event-based) (object/tree based) (pull-based / object + tree) – Lots of XML parsers and interface software available • Unix, Linux, Windows 2000/XP, Z/OS, etc – SAX-based parsers are fast (often as fast as you can stream data) – DOM slower, more memory intensive (create in-memory version of entire document – Validating can be much slower than non-validating IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 20

Parser API: SAX A) SAX: Simple API for XML – http: //www. megginson. com/SAX/index. html – An event-based interface (a push parser API) – Parser reports events whenever it sees a tag/attribute/text node/unresolved external entity/other (driven by input stream) – Programmer attaches “event handlers” to handle the event · Advantages – Simple to use – Very fast (not doing very much before you get the tags and data) – Low memory footprint (doesn’t read an XML document entirely into memory) · Disadvantages – Not doing very much for you -- you have to do everything yourself – Not useful if you have to dynamically modify the document once it’s in memory (since you’ll have to do all the work to put it in memory yourself!) IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 21

Parser API: DOM B) DOM: Document Object Model – – http: //www. w 3. org/DOM/ An object-based interface Parser generates an in-memory tree corresponding to the document DOM interface defines methods for accessing and modifying the tree · Advantages – Very useful for dynamic modification of, access to the tree – Useful for querying (I. e. looking for data) that depends on the tree structure [element. child. Node("2"). get. Attribute. Value("boobie")] – Same interface for many programming languages (C++, Java, . . . ) · Disadvantages – Can be slow (needs to produce the tree), and may need lots of memory – DOM programming interface is a bit awkward, not terribly object oriented IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 22

DOM Parser Processing Model DOM parser interface XML data application parser Document “object” desc text order partorders quantity delivery-date order IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 23

Parser API: JDOM B 2) JDOM: Java Document Object Model – – http: //www. jdom. org A Java-specific object-oriented interface Parser generates an in-memory tree corresponding to the document JDOM interface has methods for accessing and modifying the tree · Advantages – Very useful for dynamic modification of the tree – Useful for querying (I. e. looking for data) that depends on the tree structure – Much nicer Object Oriented programming interface than DOM · Disadvantages – Can be slow (make that tree. . . ), and can take up lots of memory – New, and not entirely cooked (but close) – Only works with Java IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 24

Parser API: Pull C) Pull Interfaces – http: //www. xmlpull. org/ (Java); there is also a. NET pull API – An pull-parser interface – API uses expressions / methods to ‘pull’ specific chunks of XML data, or to iterate over the XML – Can be built on top of a DOM model · Advantages – Easier to write applications that need to read in and process XML data (‘easier’ model than a push API, in many cases) – Has proven a very popular component in the. NET toolkit · Disadvantages – Can be slow if you do lots of iteration over the XML input data – No common API across different languages (although xmlpull. org tries to be similar to the. NET API); not yet a ‘real’ standard (still being worked on; not part of most commercial environments) IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 25

XML Processing: XSLT D) XSLT e. Xtensible Stylesheet Language -- Transformations – http: //www. w 3. org/TR/xslt – An XML language for processing/transforming XML – Does tree transformations -- takes XML and an XSLT style sheet as input, and produces a new XML document with a different structure · Advantages – Very useful for tree transformations -- much easier than DOM or SAX for this purpose – Can be used to query a document (XSLT pulls out the part you want) · Disadvantages – Can be slow for large documents or stylesheets – Can be difficult to debug stylesheets (poor error detection; much better if you use schemas) IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 26

XSLT processing model · D) Processing model schema XSLT style sheet in XML data in XSLT processor XML parser data out (XML) XML parser document “objects” for data and style sheet schema order partorders desc text part quantity delivery-date order IT Strategy, IBS, Technology & Solutions xza partorders foo bee order ian. graham@bmo. com / 416. 513. 5656 27

XML Processing Toolkits Lots of them … · Java – JAXP dom 4 j. NET … ( http: //java. sun. com/xml/jaxp/faq. html ) ( http: //www. dom 4 j. org ) ( part of. NET framework) … others … · Provide DOM, SAX, (JDOM) interfaces, plus lots of other useful tools in a standardized way (loading parsers, performing XSLT transformations, etc. ) · JAXP is standard Java, and thus integrated with Websphere IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 28

XML and databases · So where do you stick XML data – Inside a database!? ! – But how to do this – and which database type to use: – RDBMS, ODB, XML? ? · How you do so depends on the use cases you have for the data. Some good-to-ask questions are – Am I talking about storing documents, or data? – Is the XML format integral to the application (e. g. XHTML, Doc. Book? ) – How will the database be queried? – Queried by XML structure, or by standard SQL – What ‘parts’ of the document need to be queried – Do I need a text index? – How will the data be used/retrieved? – Passed to XML processing tools (e. g. XSLT), or used at ‘atomic’ simple type level? – The answers drive out – What database to choose, how to map XML to tables (O-R or table mappings), store as BLOB or broken up …. . IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 30

XML and databases · Upcoming technologies – XML Query – a query language for querying XML datasets (and databases) • Uses XML schema for type casting, and validation • Info: http: //www. w 3. org/XML/Query · Useful XML Database references – – http: //www. xml. com/pub/a/2001/10/31/nativexmldb. html http: //www. rpbourret. com/xml/XMLAnd. Databases. htm http: //www. rpbourret. com/xml/XMLDatabase. Prods. htm http: //www. xmldb. org/resources. html IT Strategy, IBS, Technology & Solutions Introductory article XML and databases Products list Docs / resource list ian. graham@bmo. com / 416. 513. 5656 31

XML Messaging · Use XML as the format for sending messages between systems · Advantages: – Common syntax; self-describing (easier to parse) – Can use common/existing transport mechanisms to “move” the XML data (HTTP, HTTPS, SMTP (email), MQ, IIOP/(CORBA), JMS, …. ) · Requirements – Shared understanding of dialects for transport (required registry [namespace!] ) for identifying dialects – Shared acceptance of messaging contract · Disadvantages – Asynchronous transport; no guarantee of delivery, no guarantee that partner (external) shares acceptance of contract. – Messages will be much larger than binary (10 x or more) [can compress] IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 33

Common messaging model · XML over HTTP – Use HTTP to transport XML messages – POST /path/to/interface. pl HTTP/1. 1 Referer: http: //www. foo. org/my. Client. html User-agent: db-server-olk Accept-encoding: gzip Accept-charset: iso-8859 -1, utf-8, ucs Content-type: application/xml; charset=utf-8 Content-length: 13221. . . . . . Markup in message. . . IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 34

Some standards for message format · Define dialects designed to “wrap” remote invocation messages · XML-RPC http: //www. xmlrpc. com – Very simple way of encoding function/method call name, and passed parameters, in an XML message. · SOAP (Simple object access protocol) http: //www. soapware. org – More complex wrapper, which lets you specify schemas for interfaces; more complex rules for handling/proxying messages, etc. This is a core component of Microsoft’s. NET strategy, and is integrated into more recent versions of Websphere and other commercial packages. W 3 c activity (who sets the SOAP spec) is outlined at: http: //www. w 3. org/2000/xp/Group/ IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 35

XML Messaging + Processing • XML as a universal format for data exchange Application SOAP API Factory Place order SOAP interface (XML/edi) using SOAP over HTTP Supplier SOAP Supplier XML/ EDI Transport HTTP(S) SMTP other. . . IT Strategy, IBS, Technology & Solutions Supplier Response (XML/edi) using SOAP over HTTP ian. graham@bmo. com / 416. 513. 5656 36

Web “Services” Model · SOAP plus higher-level modeling for how services are ‘advertised’, ‘exposed’ and ‘found’ – Uses an XML dialect, WSDL (Web Services Description Language) to define a service • WSDL can use XML Schema to define how data is passed between a service provider and requestor – Uses an XML dialect, UDDI (Universal Description, Discovery and Integration) for • Describing services (high-level) • Discovering services (registry services, metadata) • UDDI defined using XML Schema – Core technology for application integration • • Microsoft. NET IBM Websphere Oracle …. Many others IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 37

Web Services Code Development Client code XML schema proxy automated code generator skeleton proxy Write the Application! WSDL WS/SOAP Requests/ responses WS/SOAP skeleton Validation, business logic, routing, Logging, more… Middle tier code adapter MECH IT Strategy, IBS, Technology & Solutions Product System code ian. graham@bmo. com / 416. 513. 5656 38

W 3 C rec W 3 C draft XML (and related) Specifications XML Core XML 1. 0 industry std ‘Open’ std Xfragment XML names RDF Canonical Xpath Math. ML APIs XSLT JDOM Xpointer SMIL 1 & 2 XML base SVG JAXP DOM 1 DOM 2 DOM 3 Xlink XSL XML signature Style XHTML events UDDI Biztalk XML-RPC eb. XML WDDX . . . XMI IT Strategy, Protocols& Solutions IBS, Technology Web WSDL. . . Services XHTML 1. 0 Xforms XML schema SOAP CSS 2 CSS 3 …. . . XML query …. SAX 1 SAX 2 CSS 1 Infoset Modularized XHTML Fin. XML IFX Fp. ML XHTML basic dir. XML. . . 100's more. . ian. graham@bmo. com / 416. 513. 5656 Application areas 40

XML 101: A Technical Introduction to XML The End. Ian GRAHAM IT Strategy, IBS, Technology and Solutions, BMO Financial Group E: T: (416) 513. 5656 / F: (416) 513. 5590 IT Strategy, IBS, Technology & Solutions ian. graham@bmo. com / 416. 513. 5656 41