AN INTRODUCTION TO XML Well look at XidML later

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AN INTRODUCTION TO XML (Well look at XidML
later)

• SESSION 1

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THIS SESSION

• What is XML?
• History of XML
• Applications of XML
• Tools for XML (more in session 9)
• Pros and Cons of XML
• Data Interchange with XML (more in session 9)
• Later, we will discuss
• Why XidML?
• The XidML schema in detail

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WHAT IS XML?

• eXtensible Markup Language
• An industry standard language for the creation of
  structured documents
• By Marking up data we mean inserting tags (i.e.
  elements or attributes) or other information into
  the document so that it is easier to process

ltBookgt ltName typetextgtThe
Outsiderlt/Namegt ltAuthor typetextgt Albert
Camuslt/Authorgt ltCategory typetextgt
Fictionlt/Categorygt ltPublished typedategtlt/Publis
hedgt ltPrice currencyUSD Typelistpricegt
19.99lt/Pricegt ltInStock typeIntegergt4lt/InStockgt
ltDiscount typebooleangtNolt/Discountgt lt/Bookgt

• By the way This example is often used to
  illustrate XML, if this XML was developed by
  xidml.org the type attributes would be in a
  schema BooksML and the currency would be an
  Element (more later)

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XML IS MORE THAN A BETTER ASCII

• ASCII is normal text
• Human readable (evolved from typewriter)
• Many tools to manipulate it
• Can be easily converted to proprietary (e.g.
  Word, Excel)
• Plain Text - Low information

Name Author Category Published Price In Stock
Discount The Outsider Albert Camus Fiction 19.99
4 No The Road to McCarthy P. McCarthy Travel 2002
24.99 3 Yes

• No context
• No Structure
• Needs Human interpretation

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XML IS MORE THAN A BETTER CSV

• Comma Separated Variables is structured ASCII
• Human readable
• Can be easily converted to proprietary (e.g.
  Word, Excel)
• More information

Name, Author, Category, Published, Price, In
Stock, Discount The Outsider, Albert Camus,
Fiction,, 19.99, 4, No The Road to McCarthy, P.
McCarthy, Travel, 2002, 24.99, 3, Yes

• Missing Information highlighted
• Words grouped correctly
• Still no context
• Needs human intervention to import/export

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XML

• Adds context and structure

ltBookgt ltName typetextgtThe Outsiderlt/Namegt ltAu
thor typetextgt Albert Camuslt/Authorgt ltCategory
typetextgt Fictionlt/Categorygt ltPublished
typedategtlt/Publishedgt ltPrice currencyUSD
Typelistpricegt 19.99lt/Pricegt ltInStock
typeIntegergt4lt/InStockgt ltDiscount
typebooleangtNolt/Discountgt lt/Bookgt

• Context added
• Type information added
• Can be automatically manipulated
• Information rich
• Needs rule book to understand

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IF WE USED BookML
ltBook Reference "BK0001"gt ltNamegtThe XidML
handbooklt/Namegt ltAuthorsgt ltAuthor
Index"0"gt ltAuthorgtSid Emellt/Authorgt lt/Author
gt ltAuthor Index"1"gt ltAuthorgtJoe
Bloggslt/Authorgt lt/Authorgt lt/Authorsgt ltCategory
gtReferenceltCategorygt ltPublishedDategt27 March
2005 lt/PublishedDategt ltCurrencygtUsDollarslt/Curren
cygt ltAmountgt19.99lt/Amountgt ltNumberInStockgt20lt/Nu
mberInStockgt ltDiscountgtYeslt/Discountgt lt/Bookgt
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A WORLDWIDE STANDARD

• Who Controls it?
• W3C (World Wide Web Consortium www.w3.org)
• Adobe, AmEx, ATT, Boeing, Computer Associates,
  Ericcson, HP, Intel, Microsoft, Oracle, Siemens,
  Xerox etc.
• Released in 1997
• Intended as a means of distributing context rich
  documents on the internet
• A lot of information on the internet
  (www.xml.org)

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HISTORY OF XML

• XML is not new!!!!
• GML General Markup Language
• Developed by IBM in the 1960s - good for humans,
  easy manipulation
• Allowed a lot of cheatingmany variations
• SGML Standard General Markup Language
• ISO standard in 1986
• Standardized document validation and interchange
• HTML Hyper Text Markup Language
• Evolved along with World Wide Web for document
  interchange
• Loose standard
• Focus on presentation, not content or structure
• XML eXtensible Markup Language
• Addresses weaknesses of HTML
• A meta-language for defining structure and
  context
• Focus on data and data interchange
• First standard (a sub-set of SGML) released in
  1997

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TOOLS FOR XML

• XML has a lot of support tools (some free)
• Designed to be easy to develop tools
• (2 weeks for competent computer science
  graduate)
• Parsers
• Off the shelf tools for reading XML files
• Stylesheets
• A language (XSL) for transforming XML into
  other documents
• Controls how browsers display XML files
• Validators
• Checks XML files for correct structure and syntax
• Checks field values for range, format etc.
• Needs to be told what the XML structure should be
  (Schema)
• Editing Tools
• Graphical environments that integrate other tools
• Allows XML, schema, stylesheets to be developed
• Validate files with strong error checking

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ADVANTAGES

• Allows specialists to extend language for a
  domain
• (music, mathematics, graphics, flight test
  instrumentation)
• Self-documenting
• With a schema
• Robust, recoverable and future-proof
• XML formats are text-based, making them more
  readable, easier to document, and easier to
  debug.
• Off the shelf tools
• Tools are available on different platforms,
  making it simpler to use XML instead of binary
  formats to exchange complex information streams.
• Maps very well onto structured data (e.g.
  databases)
• Allows creation of own-labelled structures for
  storing information.
• Well understood and supported

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DISADVANTAGES

• Different specialists developing different
  standards!
• Can be made incomprehensible and proprietary
• Yet another language with a learning curve
• Files can be large
• Not (inherently) an indexed medium
• No native support for libraries and nested files
• No native support for archiving and revision
  control (of the data as opposed to the schema)

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APPLICATIONS OF XML

• XML is good for
• Data interchange between computers, platforms and
  applications
• Representing structured data for automated
  processing
• Future-proofing data
• XML is not good for
• Data storage/exchange in a homogenous environment
• It is not a Database (despite the hype!)

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EXAMPLE - PROBLEM
Test Vehicle
Ground
Flight Test DAU
Ground Station
Vendor 1 Database
Vendor 2 Database
Same information (or a subset) required in each
place Different database structures Different
vendors
FTE
Test Config Database
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EXAMPLE SOLUTION 1
Test Vehicle
Ground
Flight Test DAU
Ground Station
Vendor 1 Database
Vendor 2 Database
Custom SQL Application
Custom SQL Application
Database structure cannot change Very static No
flexibility Hard to maintain Must learn database
mapping for each vendor
FTE
Test Config Database
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EXAMPLE SOLUTION 2
Test Vehicle
Ground
Flight Test DAU
Ground Station
Vendor 1 Database
Vendor 2 Database
Must learn to write/read a new format for each
vendor Must learn database mapping for each
vendor Freedom to change databases
FTE
Test Config Database
Proprietary File Format
Proprietary File Format
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EXAMPLE SOLUTION 3
Test Vehicle
Ground
Flight Test DAU
Ground Station
Tools available to Assist XML transformation
Vendor 1 Database
Vendor 2 Database
XML I
Must learn database mapping for each
vendor Freedom to change databases Read/Writing
significantly easier
FTE
Test Config Database
XML III
XML II
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EXAMPLE SOLUTION 4
Test Vehicle
Ground
Flight Test DAU
Ground Station
Vendor 1 Database
Vendor 2 Database
XML
Must learn database mapping for a single XML
file Freedom to change databases Read/Writing
significantly easier
FTE
Test Config Database
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SO FAR

• XML A world standard for data interchange
• A better ASCII
• Community of XML developers for support and
  development
• Not a database - but closely tied to databases
• An optimal solution to the problem of data
  interchange
• Development effort still required

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XML SCHEMAS

• Specifies the grammars for an XML document
• Provides a description of the document structure
  and meaning (meta-meta-data)
• A schema is necessary and sufficient to fully
  describe an XML grammar
• Provides support for development and
  documentation
• Tools exist to automatically build data model
  diagrams from a schema
• Tools exist to automatically compare an XML
  document against its schema and test for validity
  (or not)
• A schema can consist of many sub-schema that
  provide descriptions of sub-sets of the document.
• When we talk about a specialist implementation of
  XML we really refer to a publicly released schema
  for that domain
• MathML for mathematics
• SensorML for sensors
• XidML for data acquisition and processing

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XML STYLESHEETS (XMLT)

• XML stylesheets can be used to transform XML
  documents to almost any target format
• Best used for XML or HTML target formats
• Can avoid coding with a parser
• Stylesheets are all about presentation
• Single source document can be used to generate
  different reports for different audiences
• An XML transform can be applied to an XML
  document by including a Stylesheet processing
  instruction  
• Single line added before the XML node
• Any program that understands XMLT (such as
  Internet Explorer) can use the stylesheet to
  transform the XML into the target format.

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XPath

• Used as a general-purpose query notation for
  addressing and filtering the elements and text of
  XML documents
• Usually used in conjunction with XMLT (or a
  parser) to extract data from a source XML
  document and transform this data to a different
  format
• Allows tools for searching XML files to be built

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DATA, META-DATA, AND
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DOCUMENTING XML

• Sources of information
• The schema
• A structured description of all possible
  elements, acceptable data types and values
• The documentation
• Word document or HTML file with graphical
  description of elements
• Useful when programming

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THE SCHEMA

• The schema
• A structured description of all possible
  elements, acceptable data types and values
• Actually, there are many files they combine to
  describe the schema
• Not really for humans to read - more useful when
  used in conjunction with a tool like XMLSpy

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THE SCHEMA - TREE
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THE SCHEMA - GRID
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XML DOCUMENTATION

• Usually HTML or Word document
• Every element is described
• Data model diagrams provide a lot of information
  about the element
• Can drill down into more and more detail as
  required
• Provides information on cross-referencing

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DATA MODEL DIAGRAM - FRAGMENT
Dotted line indicates optional element
indicates contains hidden child elements
(click to expand)
Indicates number of instances allowed
Connector indicates a sequence, a choice or all
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DATA MODEL DIAGRAM - EXAMPLE
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THREE VIEWS OF THE SAME DATA
Schema Documentation
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ATTRIBUTES AND ELEMENTS
ltDataLinksgt ltDataLinkSetgt ltX-DataLink-1.0
Name"MyRS232_Link1"gt ltDataBitsPerWordgt8lt/Data
BitsPerWordgt lt/X-DataLink-1.0gt lt/DataLinkSetgt
lt/DataLinksgt
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THIS SESSION COVERED

• What is XML?
• Main elements of XML
• How XML is documented
• Next, we will talk about XidML

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END OF SESSION 1