DT050 Using XML in COBOL applications

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DT050Using XML in COBOL applications

• Barry Rosetti
• 01 March 04

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What is this presentation

• Overview of XML and how it is used.
• Handling XML in Micro Focus COBOL
• Syntax elements and their usage
• Basic and advanced manipulation
• Handling XML with IBM extensions
• Syntax elements
• Comparison with MF extensions
• Resources, etc

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What is XML?

• A (very) flexible data encoding schema
• An XML document has
• Optionally, an XML version and (explicit)
  encoding
• Optionally, a document type definition (DTD)
• A hierarchy of tags and values with one root tag
• Optionally, associated with tags attributes and
  their values
• Optionally, comments and extra info (processing
  instr)
• A basic XML document
• Tag docs
  value

DT050 Barry Rosetti 01 March 04
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How is XML used?

• Extended, leveraged and used in n different ways
• Namespaces, Schemas, XSLT, XPATH, XLINK,
  Xanything
• As time goes by, n grows (and grows)
• Basic extensions for XML usage
• Namespaces
• Allow complex documents from multiple sources
• Schemas
• Allow rigorous checking of document validity
• Some other extensions push the envelope
• Making XML an awkward programming language

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How does one handle XML in COBOL?

• Theres nothing new under the sun
• XML Document types have strong similarities to
• COBOL Record Structure
• Pascal Records
• C Structs
• But XML Document are more dynamic
• Unlimited occurrences
• Recursive

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How does one handle XML in COBOL?

• Use syntax to handle XML documents and schemas
• Define file that represents an XML I/O stream
• Define records that correspond to XML document
  structure
• Open file, and perform I/O operations on it
• Single-shot or dynamic document manipulation
• Use IBMs XML parse syntax (mainframe)
• With a fixed buffer, start a SORT style input
  procedure
• Retrieve document tag, attribute and value
  at-a-time
• Low-level parsing of document

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MF Syntax - SELECT

• SELECT statement is the foundation
• Just like COBOL File I/O
• Assign a COBOL name to the file
• Assigns a source or sink for the I/O stream
• Describes what the file is all about
• Organization type for validation
• Tells you where you get the file status
• SELECT xml-bookdb ASSIGN "cbookrw.xml
• ORGANIZATION IS xml
• DOCUMENT-TYPE IS "bookdb.xsd"
• FILE STATUS IS xml-bookdb-status.

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MF Syntax - SELECT

• ASSIGN is source or sink
• Can be a literal or variable file - c\foo or
  fname-data-item
• Can be a memory buffer address of mybuff
• Can be a pointer to a buffer ptr-to-buf length
  is buf-len
• DOCUMENT-TYPE is Schema (not DTD!)
• Can be a literal or variable xsd foo.xsd or
  xsd-data-item
• On input is not validated (will be optional in
  future)
• On output decorates the root tag with attributes
• xmlnsxsi"http//www.w3.org/2001/XMLSchema-instan
  ce" xsischemaLocationfoo.xsd
• FILE STATUS is PIC S9(9), values 0 are success
• You must declare in your working storage section

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MF Syntax - XD

• XD and all of its records
• The association between XML and COBOL records
• The following
• xd xml-bookdb.
• 01 xml-bookdb-query identified by
  "query.
• 05 xml-bq-author pic x(40) identified by
  "author".
• 05 xml-bq-title pic x(40) identified by
  "title".
• represents an XML document that has structure
• Author Name
• Book Title

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MF Syntax - XD

• Lots and lots of things you can do in an XD
  record
• IDENTIFIED BY either literal or variable
• identifies tag this item will produce or receive
• IS ATTRIBUTE
• specifies that this isnt a tag, but is a
  contained attribute
• COUNT IN implicitly defined data item
• specifies occurences read or written
• NAMESPACE IN either literal or variable
• allows qualification of namespace
• IS PROCESSING-INSTRUCTION
• allows reading or writing of items

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MF Syntax - XD

• Worthwhile discussing variable tag/attr/ns names
• 01 foo identified by foo-tag-name namespace is
  foo-ns-name.
• 05 foo-tag-name pic x(80).
• 05 foo-ns-name pic x(80).
• 05 foo-value pic x(80).
• 05 foo-attr identified by foo-attr-name
• is attribute.
• 10 foo-attr-name pic x(80).
• 10 foo-attr-value pic x(80).
• Variable tags are directly contained in group

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MF Syntax Basic Verbs

• OPEN inputoutputi-o file-name
• surprise, surprise, surprise
• READ file-name
• Read entire XML document
• WRITE file-record
• Write entire XML document
• CLOSE file-name
• more surprises

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MF Syntax Extended Verbs

• These are where the power is
• When an XML document is read
• Internal representation of document created
• Record populated as possible
• When an XML document is written
• Internal representation of document is written
• In basic WRITE, from record to internal to output
• In extended WRITE, from record to internal
• Final WRITE goes from internal to output

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MF Syntax Extended Verbs

• READ, WRITE, REWRITE, DELETE, START
• All have KEY IS phrase
• KEY IS an IDENTIFIED BY item
• With every IDENTIFIED BY item
• Corresponds to a node in internal
  representation
• There is a current node in internal
  representation
• Operation happens wrt this current node
• Operation then updates this current node

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MF Syntax Extended Verbs example

• 01 foo-record identified by tag.
• 05 foo-attr identified by foo-attr-name
• is attribute.
• 10 foo-attr-name pic x(80).
• 10 foo-attr-value pic x(80).
• OPEN foo-file
• READ foo-file populate internal representation
• START foo-file KEY IS foo-attr INDEX IS 2
  start at second
• READ foo-file NEXT KEY IS foo-attr
  get name val
• DISPLAY foo-attr-name foo-attr-value ---
  cool!!

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MF Syntax Extended Verbs example

• Given input of
• /
• Will display
• attr2nameattr2value --- cool!!
• Same sort of thing works on OUTPUT and I/O
• Dynamically move through internal representation
• And modify as you go
• And a final write will create the document

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MF Syntax Extra bits

• WRITE KEY IS PROCESSING-INSTRUCTION
• Allows dynamic insertion of a processing
  instruction, eg
• READ Pis with IS PROCESSING-INSTRUCTION in record
• WRITE KEY IS PLAIN-TEXT
• Allows dynamic insertion of plain text, eg
• Content-type text/xml
• These work outside of document body
• and also inside from position of last operation

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MF Syntax Things to know

• Syntax implemented as preprocessor (for now)
• set preprocess(prexml) endp
• If error in XML source code
• Preprocessor will abandon source substitution
  and
• Checker will give a lot (lot) more errors
• Always (always) use WARN directive
• set preprocess(prexml) WARN endp
• set preprocess(prexml) WARN OUT(ppcode.cbl) endp

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MF Syntax Interesting example

• Parse an arbitrary XML document
• Allowing maximum depth of 1 nested tags (for
  simplicity)
• Replace all attribute values yes with no
• Write document
• Watch it go

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IBM Syntax XML Parse

• Given a buffer, parse it a bit at a time
• xml parse buff processing procedure is routine
• goback.
• routine section. called n times, where n is
  large
• Handle xml-events
• exit section.
• Special registers for use in routine
• XML-EVENT name
• XML-TEXT
• XML-EXCEPTION

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IBM Syntax Interesting example

• Parse an XML document for a sandwich
• Ham amp turkey
• Cheese,lettuce,tomato,etc.
• element!
• 4.99
• 0.10
• Note PIs, entity references, CDATA

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IBM Syntax Interesting example

• Notes
• Every last bit of input data is reported
• Content for item arrives in drips and drabs,
• building entire data is a bit tough
• Manual conversion of data into numeric formats
• Hierarchy is difficult to handle
• You have to be very familiar with XML to use
• Hmmm thats a lot of code isnt it?
• What does it look like in MF Syntax?

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General Things to know

• XML Documents are default encoded in ASCII
• You can modify this with PI
• Example with MF Syntax
• Shift-jis handling with READ/WRITE
• Example with XML PARSE
• Shift-jis handling with XML-PARSE
• NetX and ServerX have CBL2XML
• Automatic conversion from XSD to COBOL record
• Automatic conversion from COBOL record to XSD
• Validate XML streams

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Resources

• Reading list and Web links
• Really good XML links
• The manual!
• http//www.xml.com/axml/axml.html
• http//www.rpbourret.com/xml/XMLURLs.htm
• IBM XML extensions
• IBM's Enterprise COBOL for z/OS and OS/390 -
  Programming Guide
• IBM's Enterprise COBOL for z/OS and OS/390 -
  Language Reference
• Contact information
• Barry.Rosetti_at_microfocus.com

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Questions?