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DTL Project 4: Transporting Time Series Observation Data with the Geograhy Markup Language with the Simple Feature Profile via a Simple Web Feature ServiceThis project has concluded. For detailed findings, see the final report.
OverviewThe mission of the Data Transport Laboratory (DTL) is to support the employment of data transport technologies that are compatible with Ocean.US Data Management and Communications (DMAC) guidance at the local and regional levels. This is accomplished through the identification, evaluation, and documentation of relevant data transport technology candidates. In following that mission, the DTL is exploring the use of the Open Geospatial Consortium (OGC) Web Feature Service (WFS) and the Geography Markup Language (GML) Simple Feature Profile to transport in-situ time series data. The WFS specification is a REST based XML data transport architecture. It provides a rich set of low-level services to query, acquire and manipulate geographic features between a server and client. The transport XML dialect used by the WFS is the GML. To foster a more rapid adoption of GML and the services that utilize it, the OGC recently released a new specification called the Simple Features Profile (SFP). This utilizes a more concise and thus more easily used subset of GML. This test cycle will address two basic questions. First, does the GML offer a library of XML structures capable of meeting basic or advanced data modeling needs for time series data? And second, does the WFS specification, as implemented in the test service (microWFS), provide the services necessary to query and retrieve time series data? The DTL has built two implementations of a simple WFS or microWFS: one as a Java Servlet which queries data from a Microsoft SQL Server database, and a second which is a Perl Common Gateway Interface application which queries data from a PostgreSQL database. Both query data from a simple database view which is specified by the DTL.  General microWFS Architecture Note that the function and output of the two services is identical. Further, they are not fully compliant with the WFS specifications as they only provide one method and basic error responses. There are several mandatory elements of the WFS specification that have been negelected such as the getCapabilities method. These WFS implementations are intended solely as tools to facilitate the exploration of using GML/SFP and the WFS to deliver time series data. Project SelectionSuggestions for candidate technologies to be implemented in the DTL are accepted from the Integrated Ocean Observing System (IOOS) community. The primary sources for the identification of candidates are the local observatories, regional associations, Ocean.US Data Management and Communications (DMAC) team and its expert teams, and deliberate outreach efforts of the DTL staff, such as meetings and workshops. Candidate technologies, identified through these mechanisms, are filtered through a set of criteria to assess their relevance and importance to the stakeholders. For more details, read about the DTL technology selection process. The selection of the this project is consistent with the DMAC guidance which espouses a Web Services approach and identifies Open Geospatial Consortium (OGC) specifications as relavent. The DTL implementation of the WFS (microWFS) is a Representational State Transfer (REST) based HTTP service. The following table shows the criteria and results for this project.
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DTL Server Details (top)The microWFS was installed in the DTL on a Dell PowerEdge 1850 machine with two 3.0 MHz Xeon CPUs, four gigabytes of RAM, 300 gigabytes of 10,000 RPM disks, and Gigabit network cards. The operating system is Red Hat Linux Enterprise 4, kernel 2.6.9-42. microWFS server Installation, Configuration, and Testing (top)The Java and Perl implementations each contain installation instructions. Please refer to the documents in each software bundle. The Java ServletThe Java .war file is deployed in the typical manner. It has been successfully deployed on Tomcat servers on both Windows and Linux operating systems and on a Sun Application Server running on a Windows operating system. Modifications to the servlet's context.xml and web.xml files are necessary. The instructions bundled in the download cover how to modify those files before deploying the application. Experienced Tomcat administrators may prefer to deploy the application and then modify the appropriate files. The Perl/CGI ApplicationThe Perl/CGI application runs in a typical CGI context and should run on any web server that supports CGI applications. It has been successfully installed on Apache HTTP server version 2.0 connecting to a PostgreSQL database server. Installation on other operating systems should be possible. The Perl code uses typical DBI::DBD mechanisms to connect to the database and execute SQL queries. Any database for which a DBD driver exists will likely work. The installer is responsible for installing the driver and modifying the database connection string in the Perl code appropriately. Testing and Critique with External Partners (top)The DTL solicited participation in the testing and critiquing of this technology from external partners. The external partners will install, configure, and run instances of the micorWFS service. Objective speed and through-put tests will be performed, and more subjective issues will be discussed and reported. Once the test phase is complete, the DTL will compile the test results and commentary in a report that will be available on the DTL Web site and on the Community Information Repository. |
