1. Datatypes for OGSA Dr Martin Westhead Principal Consultant, EPCC Telephone:+44 131 650 5958 Fax:+44 131 650 6555 Email:M.Westhead@epcc.ed.ac.uk

2. Overview Uses of XML Basic types Complex types Binary File Description Discussion – feedback.

3. Uses of XML Two distinct areas: Meta data – input values, algorithm choices etc. Real datasets – large scale datasets More interest in (1) – natural use of XML Some interest in (2) but: –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

4. 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

5. 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

6. 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?

7. 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 Big/little endian Precision Offset Record separators…etc –Higher level structure Array dimensionality/size Variable names

8. Discussion Feedback? What do you/your users want to use XML for? Value of standard binary description?

9. NeSC registry XML schema references (Yahoo!) XML schema mirrors UDDI registry of eScience Grid Services