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WFS DataStore Design

Prepared by:

David Zwiers, Refractions Research

Introduction

For the upcoming uDig project we intend to create a WFS DataStore following the GeoTools DataStore API. This document outlines an overview of the design for the proposed DataStore, as well as documenting the effects this will have on other GeoTools modules.

Module Overview

Currently GML is parsed using the GMLDataSource. It is my understanding that this is to be phased out. As such I intend to create a new module with a set of GML parsers, GML Writers, a GMLDataStore and a WFSDataStore. An overview of the module interactions can be seen in the following diagram:

As can be seen in the preceding diagram, the GMLDataStore and WFSDataStore both use the GML parsers and writers. We can also see that there is not a functional dependence between the parsers and writers, or the GMLDataStore and the WFSDataStore.

Schedule

GMLDataStore for Milestone 1 / Geotools 2.0 rc1
WFSDataStore for Milestone 2 / Geotools 2.1 branch

GML Parser

For the use of GML Datastore and WFS Datastore our parser is required to handle the following:

  • Feature
  • Geometry
  • Filter

To further handle the needs of a WFS DataStore our parser will be extended to handle:

  • FeatureType

Our parser can be extended with additional GML 2.1 constructs as required.

Other non-functional development goals for this module include:

  • Scaleable
  • Streamable

Parser Class Diagram

At this time we envision the GMLParser module to resemble the class structure depicted in the following Figure.

GML Writer

Although a complete GML Writer is not required, our parser should as a minimum print the following GML 2.1 constructs:

  • Feature
  • Geometry
  • Filter

The GeoServer project will require this library provide:

  • FeatureType

Other non-functional development goals for this module include:

  • Scaleable
  • Streamable

Writer Class Diagram

At this time we envision the GMLWriter module to resemble the class structure depicted in the following Figure.

GMLDataStore

The GMLDataStore is intended to provide access to GML parser/writer in a convenient way. For the most part, the GMLDataStore will be a wrapper for the GML parsers and writers. The GMLDataStore is intended to be OGC GML 2.1 compliant.

GMLDataStore functional requirements:

  • GML 2.1 Compliant
  • Reads/Writes from a URL
  • Parses/Writes results made available via GMLFeatureReader/GMLFeatureWriter

GMLDataStore Class Diagram

At this time we envision the GMLDataStore module to resemble the class structure depicted in the following Figure.

WFSDataStore

The WFSDataStore is a new module indented to communicate with OGC compliant WFS servers. This module will make extensive use of the GML parsers, and will implement the DataSource API.
WFSDataStore functional requirements:

  • WFS 1.0.0, GML 2.1 Compliant
  • Reads and Writes to a WFS
  • Parses and Writes WFS Requests
    • GetCapabilities
    • DescribeFeatureType
    • GetFeature
    • LockFeature
    • Transaction

WFSDataStore non-functional requirements:

  • Scaleable
  • Streamable
  • Self-initializing

WFSDataStore Class Diagram

At this time we envision the WFSDataStore module to resemble the class structure depicted in the following Figure.

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