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Introduction. Two components Data Exchange Infrastructure (DEI) Spatial Data Model (SDM) Together, they make up “NCDDC Middleware”. Introduction to NCDDC Middleware - what it does and why. Richard Owens. What Is DEI (High-level overview).

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  • Two components

    • Data Exchange Infrastructure (DEI)

    • Spatial Data Model (SDM)

  • Together, they make up “NCDDC Middleware”

What Is DEI (High-level overview)

DEI is a client/server framework by which applications and data repositories can interact. The goal of the framework is to solve the problems of Data Access and Data Representation.

DEI is a CORBA-based set of interfaces which are used to locate and transfer geospatial data. It is a client/server architecture which uses CORBA's IIOP (uses TCP) as its transport protocol.


DEI Concepts

  • Gateway

    • Server component that adapts DEI interfaces to a specific

    • data source

  • Data source dependent

  • DEI Client

    • Any software that uses DEI CORBA interfaces to

    • communicate with gateways




DEI Concepts (continued)

  • Data Flavor (formats)

  • Like a MIME type

  • What DEI Is Not


    • Lacks generic query processing

    • Poor support for very large datasets

    Data Archive/Storage

    Data Format

    • Supports them, though

    Web services

    (graphic here)


    Originally Navy NRL funded project

    Now being developed by NCDDC

    Current Status

    Java based gateways via Java GDK

    Current focus

    C++ gateways

    Original focus, now lagging behind Java


    Mature Java GDK, then C++ GDK

    Add generic query processing

    Add support for very large datasets

    Open source

    • What is the SDM

    • Object-oriented library that is used to represent and manipulate spatial data objects.

    • 3D

    • Some other dimensional capabilities, too

    • Structured Grids

    • Regular, Rectilinear, Curvilinear, Projected

    • Unstructured Grids

    • Coordinate Systems

    • Cartographic, Cartesian, Cylindrical, Spherical

    • GIS-like structures

    • Points, Lines, Polygons, etc.

    Key Features

    • Called the “Field Spatial Data Model” by its developer because it uses a ‘field’ concept, which relates spatial objects to data.

    • Fundamental storage is multi-dimensional array.

    • Decoupling of data storage from its geometry and topology.

    • Requires basic metadata (quantity, units, validity, accuracy, etc.) for all data.

  • Aids in interoperability

  • Key Features (continued)

    • Small, consistent API for data access.

    • The SDM hides all implementation details of data representation behind its abstract interfaces.

    • Decouples many issues regarding storage and internal representation of the data, while providing a consistent interface to it.

    • Data may be logically represented one way and physically stored another way.

    • Many manipulations may be done without actually having to have the data physically in memory.

    Key Features (continued)

    • Externalized format for representing datasets

    • XML based (FDML)

    • Can be generated without the use of the SDM.







    Field Concept

    What SDM Is Not

    Transport mechanism


    Magic. Won’t solve all problems.

    Just a data format


    • History

      • EPA project

      • Ported from Eiffel to Java in 2002

    • Future

    • Documentation

    • FY03

      • Text data (done)

      • Generalize dimensional support beyond existing 3-D

    • (to 2-D, 1-D or N-D)

      • Investigate Time dimension support (complete in FY04)

      • Application Layer Services

    • Common Query mechanism

    • Subsetting (parameters, spatial)

    • Format support (NetCDF, Shapefile)

    • FY04

    • Aggregation of data types

    • Time dimensions support - including subsetting in

    • Application Layer

    • Open Source

    NCDDC Middleware Objective

    Develop a middleware architecture that can be used to tie data and applications together across a local or wide-area network in a way that is independent of the data and application platforms, operating systems, and formats.

    • NCDDC Middleware Defined

    • “NCDDC Middleware” is the fusion of DEI with SDM

    • DEI

    • Data Transport

    • SDM

    • Data Representation

    • DEI + SDM (“NCDDC Middleware”)

      • Spatial data representation distributed over a network

      • Common form for data, and the means for transporting it

    DEI/SDM, HTTP/HTML Analogy





    • Benefits

    • Gateways can be created that can transport descriptions of the data with embedded links to the actual data – the actual transport of the data is done piecewise, “on demand”.

      • Can have datasets that are larger than memory.

      • Caching mechanism improves performance.

    • Data is transported in binary form

      • Sun’s XDR format

    • Foundation for netCDF

      • Fast and efficient

    • Since DEI is integrated within the SDM, clients can use SDM interfaces to access gateways without the need to code to DEI’s CORBA interfaces.