Publication Date: 2018-01-08
Approval Date: 2017-12-07
Posted Date: 2017-10-31
Reference number of this document: OGC 17-037
Reference URL for this document: http://www.opengis.net/doc/PER/t13-NG005
Category: Public Engineering Report
Editor: Jeff Harrison
Title: OGC Testbed-13: SWAP Engineering Report
Copyright © 2018 Open Geospatial Consortium. To obtain additional rights of use, visit http://www.opengeospatial.org/
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- 1. Summary
- 2. References
- 3. Terms and Definitions
- 4. Overview
- 5. Experiments
- 6. Findings and Recommendations
- Appendix A: Revision History
- Appendix B: Bibliography
This OGC document provides an analysis of the prototype implementations, approaches and performance aspects of data serialization techniques explored in OGC Testbed 13. Specifically, it describes work done during Testbed 13 investigating serialization for geospatial data sets on OGC Web Feature Service (WFS) using Google Protocol Buffers (Protobuf) and Apache Avro.
The OGC WFS provides an interoperable method to access and update geodata across network-connected components. However, results from previous OGC activities and operational deployments indicate that transferring large volumes of geodata from a WFS over a network with poor or very low bandwidth can take a significant amount of time, and network capacity.
To help meet this challenge OGC Testbed 13 developed prototype implementations and conducted Technology Integration Experiments to assess optimizing data transfer under bandwidth-constraint conditions. This document discusses geospatial data size reduction techniques, focused on enhancing WFS for serialization using Google Protocol Buffers and Apache Avro.
1.2. Prior-After Comparison
This Testbed 13 work builds on experiments conducted in Testbed 12 investigating compression for geospatial data sets on OGC Web Feature Service (WFS) using W3C Efficient XML Interchange (EXI) Format 1.0 (Second Edition). This document is available at the following link -
Testbed 13 Technology Integration Experiments used the same test data sets as Testbed 12, allowing comparison of the results.
1.3. Technology Integration Experiments
In OGC Testbed 13 participants investigated serialization techniques for geospatial data sets delivered by WFS Servers and Clients by augmenting WFS with software capable of producing output as a serialized object.
The testing architecture for this part of OGC Testbed 13 was configured using a combination of the following data and components:
Vector Data - Feature data over San Francisco representing points (schools_public_pt.shp), lines (stclines_streets.shp) and polygons (schools_public.shp) formed the test baseline.
Serializer/Deserializer - Component that writes and reads data in the 'protocol buffers' serialization format engineered by Google or Avro.
SWAP WFS - WFS augmented with the ability to write vector data into a serialization format.
SWAP WFS Client - Application clients with the ability to request serialized data from a SWAP WFS, using an outputFormat query parameter, with a performance recording module to gather metrics on the size of the resulting serializations.
These components were configured for testing as described in the following sequence diagram:
For compression testing The Carbon Project implemented SWAP WFS, SWAP WFS Clients and Serializer/Deserializer in the following architecture -
The SWAP WFS was based on CarbonCloud WFS, extended with Protobuf capability using protobuf-net. protobuf-net is a contract based serializer for .NET code, that writes data in the 'protocol buffers' serialization format engineered by Google. The API follows typical .NET patterns (it is broadly comparable, in usage, to XmlSerializer, DataContractSerializer, etc).
Feature data over San Francisco representing Points (schools_public_pt.shp), Lines (stclines_streets.shp) and MultiPolygon (schools_public.shp) formed the test baseline.
The first step in the development process involved creating objects to serialize structured data. To do this, The Carbon Project developed a description of the data structure needed for Point, Line and MultiPolygon Features. From that, a class can be created that encodes the data with a binary format. The generated class will provide the fields that make up the object and takes care of the details of reading and writing the structure as a unit.
The client was developed to support access during testing and to gather metrics. An example using protobuf is shown below: