a prototype spatial object transfer format (sotf)
DESCRIPTION
A Prototype Spatial Object Transfer Format (SOTF). Peter Woodsford ( [email protected]) Laser-Scan Ltd., Cambridge, UK. www.laser-scan.com 6th EC-GI & GIS Workshop, Lyon, France, 28-30 June 2000. SOTF - Introduction. Many agencies now handle GeoInfo as Objects - PowerPoint PPT PresentationTRANSCRIPT
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A Prototype Spatial Object Transfer Format (SOTF)
Peter Woodsford ([email protected])
Laser-Scan Ltd., Cambridge, UK.
www.laser-scan.com
6th EC-GI & GIS Workshop,
Lyon, France, 28-30 June 2000.
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SOTF - Introduction
• Many agencies now handle GeoInfo as Objects • Spatial Object Transfer Standard• SOTF is a transfer format for geospatial data optimised
for:• transfer across ‘non-live’ connections• archive• active object store to warehouse connections
• OGC’s Geography Markup Language (GML) - both XML encoding of geospatial data
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SOTF - Introduction (cont)
• Origins in NIMA research contract• Survey of current transfer standards• Requirements specification
• neutral, industry standard technology• remedying key shortcomings
• incremental update• support for value added• flexible as regards topology• 2D and 3D (and potentially, temporal)
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What is SOTF?
• A data store imports/exports SOTF datasets, SOTF describes these processes and the demands on the data store
• Currently an SOTF dataset is an XML encoding for geospatial data • similar to GML• very similar to [the first version of] SFXML
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Use of XML
• Current prototype uses XML v1.0• parallels initial OGC offerings
• Area of rapid development• particularly for schema definition, a key part of SOTF
• Indexing not key to transfer format, but technology is emerging
• Currently verbose, but emerging compression techniques (zip does a lot)
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Why the word ‘object’?
• SOTF has an object-oriented schema with:• features and feature types• properties and data types
• SOTF supports multiple geometric properties per feature
• SOTF supports both spatial and aspatial feature types
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Why the word ‘object’?
• SOTF supports multiple inheritance of feature types
• SOTF supports light-weight, binary feature relationships
• SOTF is designed to handle complex, structured geospatial data;• it does not support methods and behaviour.
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SOTF data store requirements• Designed to work with both [object-]relational and
object-oriented data stores• An SOTF dataset always includes an explicit schema
• Currently SOTF does this with a fixed DTD
• GML profile 1 would not be suitable
• To support export of an SOTF dataset a data store• should provide feature identifiers that persist between
exports
• may provide ability to retain a previous state
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SOTF and topology support
• SOTF has no in-built topology support• However topological feature types (e.g. faces, edges
and nodes) can be described using base SOTF concepts
• To work between multiple data stores it is necessary to agree on a common ‘topological sub-schema’
• A sub-schema describes an optional, but standardised, part of the schema
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Data producers and data consumers
• These two communities have differing requirements:• large vs. small geographic extent• fixed schema vs. ad-hoc inclusion of extra data• time tabled release vs. spontaneous demand
• SOTF provides a number of mechanisms to address these differences
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Incremental update
• Level of granularity is the feature• Tag features as ‘new’, ‘modified’ or ‘deleted’• Requires persistent feature identifiers• Requires a data store to be able to ‘difference’
states
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Area-of-Interest
Data supplier
SOTF datasetData consumer
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Area-of-Interest
• SOTF works at the level of features • granularity of incremental update• granularity of references
• SOTF does not require features to be split along artificial tile boundaries
• To support ‘area-of-interest’ SOTF requires features to support the concepts of extent and dependency in the data store.
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Identifying features for export
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Identifying features for export
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Identifying features for export
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Identifying features for export
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Combining SOTF datasets
Data supplier (with pre-defined ‘tile’ structure) Pre-generated,
stock-piled, set of
SOTF datasetsData consumercombines SOTF datasets
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Value Adding
• SOTF provides rules to determine if two schema are compatible.
• Since SOTF datasets always include a schema this allows:• schema evolution at the data producer to be
communicated to the data consumer• ‘compatible’ additions to the schema to be carried out
by the data consumer in support of value-adding• update does not invalidate value-added data
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Summary - key techniques
• Incremental (or change-only) update• depends on persistent feature (object) ID’s
• Support for export ‘area-of-interest’• avoids ‘tiling’
• Can be combined at receiver• permits ‘stockpiling’ by issuer
• Supports value-adding• possible through explicit schema description
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SOTF current status• SOTF has been developed to a working prototype by
Laser-Scan under contract from NIMA• uses subset of Digital Nautical Chart data• demonstrates the key techniques
• NIMA are keen to see further development of something by somebody that addresses these requirements provided:• it is compatible with emerging standards such as GML• there is interest from a wider community
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SOTF future status
• Concepts under consideration for the evolution of GML within OGC – plays into Web access
• Possible definition of content for Transaction Encoding Specification - Interoperability
• Possible unifying role in emerging set of XML-based transfer formats - Transfer
• Up to the community!