Datatypes for OGSA
Dr Martin Westhead
Principal Consultant, EPCC
Telephone:
Fax:
Email:
+44 131 650 5958
+44 131 650 6555
M.Westhead@epcc.ed.ac.uk
Overview
Uses of XML
Basic types
Complex types
Binary File Description
Discussion – feedback.
Uses of XML
 Two distinct areas:
1. Meta data – input values, algorithm choices etc.
2. Real datasets – large scale datasets
 More interest in (1) – natural use of XML
 Some interest in (2) but:
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–
–
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Some issues with basic types (also a problem for 1)
Modifying apps to read/write XML hassle
XML layout may be inconvenient (e.g. arrays)
Why bother?
 Proposed work
– Fixes for basic types
– XML schema for describing large binary files
Basic Types I
 “XML Schema Part 2:
Datatypes”
– http://www.w3.org/TR/xmlsch
ema-2/
 Floating point:
– Decimal – arbitrary precision
decimal
– Float – IEEE 754 (32 bit)
– Double – IEEE 754 (64 bit)
– Not defined: Quadruple ??
(128 bit)
 Integers
 long
 int
 short
 byte
 nonPositiveInteger
 negativeInteger
 nonNegativeInteger
 positiveInteger
 unsignedLong
 unsignedInt
 unsignedShort
 unsignedByte
Basic Types II
Complex numbers
– Proposed W3C standard:
• http://www.w3.org/2001/03/XMLSchema/TypeLibrary-nn-math.xsd
• Uses decimals only
• Need floats/doubles
– Alternative standard:
• http://www.posc.org/ebiz/pefxml/bdoc/dt_complex.html
Proposal
– Aim to contribute to W3C complex standard
Complex Types
Arrays
– W3C proposal
• http://www.w3.org/2001/03/XMLSchema/TypeLibrary-nn-array.xsd
• Multidimensional array as a tree of lists (vectors)
• Polymorphic
– Sparse array supported in SOAP
• http://www.w3.org/TR/SOAP/ (section 5.4.2.2)
• Many alternative representations possible
What else?
– Sets, bags, graphs, meshes?
Binary File Description
 Part of metadata
– Canonical description of output
– Enables web services for:
• Conversion
• Returning part of data (e.g. slice of array)
 Different levels of description
– Accessing numbers
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•
•
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Big/little endian
Precision
Offset
Record separators…etc
– Higher level structure
• Array dimensionality/size
• Variable names
Discussion
Feedback?
What do you/your users want to use XML for?
Value of standard binary description?
NeSC registry
XML schema references (Yahoo!)
XML schema mirrors
UDDI registry of eScience Grid Services