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Blog: What does the OGC/W3C working group do?

What does the OGC/W3C working group do?

In order to enable the free sharing of spatial data on the web, the Open Geospatial Consortium (OGC) and the Word Wide Web Consortium (W3C) set up a joint working group in 2014, which aims to improve and clarify the current standards. And that is badly needed, says Frans Knibbe from Geodan Research.

In an earlier blog, I wrote about the nature of spatial data, the importance of spatial data on the web, and the fact that geo-information is in a transitional phase. Data no longer needs to be stored in closed silos, but can be freely shared. The OGC and the W3C, important organizations for geo-information and the worldwide web respectively, understand that this transition must be managed correctly. To this end, the Spatial Data on the Web Working Group (SDDWG) was set up. That was a unique occurrence: never before had the OGC and W3C worked together in this way. As such, it took a little while to find a form that suited both organizations, but, ultimately, it worked out. 

The mission

The charter is the formal document that specifies the working group’s objectives. It describes the mission and which results that are be delivered. In this blog, I want to address these objectives. The SDWWG is committed to improving and clarifying standards for dealing with spatial data on the web. And that’s badly needed, because the standards that are currently available are rather unclear. In some areas there are too many standards, for example about how a vector geometry (an ordered set of coordinates) can be coded, while in other areas there is a shortage of standardization. How to reference a coordinate system, for example, is not clear. This chaos can partly be explained by the ubiquity of spatial data. The vast majority of data that we want to use on the web has spatial aspects, which means that everyone who wants to do something with data should also do something with that spatial aspect. Many have already dealt with standardization of spatial data from the perspective of their own domain and, in some cases, they may even have done so before the web came into the picture as a platform for the exchange of data.

The OGC for geo-information experts , for example, has an extensive set of standards, which together form a complex, closed semantic system. In other domains, standards have also been developed for location, for example to express a toponym, an address, or a point location. The web, however, is an environment where all domains can come together.

What does the working group deliver?

The charter describes what the working group intends to deliver:

  • A document with usage scenarios and requirements (use cases and requirements);
  • An overview of best practices for the provision and consumption of spatial data on the web;
  • An improved version of the Time Ontology in OWL (an ontology for expressing data over time);
  • An improved version of the Semantic Sensor Network Vocabulary;
  • A facility (presumably an ontology) to share coverage data via the web;

Both the OGC and the W3C publish their results, with the latter three items in the list above having a more formal status than the first two. There is something interesting to report on each of these results.

Use scenarios and requirements serve as the foundation

The usage scenarios and the requirements to be derived from them are the basis for further work. That’s why the working group addressed and published this matter first. You can find the most recent published version here. This document contains descriptions of different usage types spatial data on the web, which we can use to derive what is needed to make the system work properly. A few important requirements are:

  • Unambiguous standards for recording spatial data, spatial relations, and spatial metadata;
  • Making spatial data linkable;
  • Making spatial data on the web findable and searchable.



Inventorying best practices

The working group is now collecting best practices that will form a second document, which will show how best to publish, find, and consume spatial data on the web. In an accessible way, of course, since it’s also intended for people who are occasionally, or laterally, involved with spatial data. The working group is looking into the extent to which the current practices regarding data on the web (including the use of JSON and simple, RESTful APIs) can be applied to spatial data. To this end, the working group is taking stock of the standards and tools available and how spatial data is now being published on the web. In case of overlap, the working group will make choices. In case of functional shortcomings - some things can’t yet be done well in any way - the working group itself will find a solution, for example in the form of cooperation with other communities to expand a certain set of web semantics.

Temporal data

At first glance, it seems strange that a working group on spatial data also deals with time. On a non-cosmic level, space and time are properties that do not necessarily go together: data can have temporal aspects, spatial aspects, or both. However, there are plenty of reasons to do so:

  1. standards for the publication of spatial data often do not lend themselves for serious, professional data applications by authorities or research institutes. This data often has a temporal aspect, for example because the things that are described are changeable.
  2. Sharing spatial data is important in sciences such as history, archeology, and geology. One of the points for improvement in temporal ontology is compatibility with time that can not be expressed via the Gregorian calendar or ISO 8601, and that’s the exact type of expressions that the historical sciences need.
  3. The OGC has already modeled the concept of time in various standards, for example for time series, which are seen as a kind of coverage - a type of spatial data.
  4. There is a lot of logical overlap between space and time, which is evident, for example, when we compare Allen's interval algebra with the DE-9IM. Similarities in time and one-dimensional space as in linear referencing may be even greater, if that’s even possible.
  5. Due to our restless earth crust, where plates move continuously, coordinate systems for geography are time-dependent.

Improving the Semantic Sensor network

Sensors have two spatial aspects. First of all, they have a location that can be fixed or variable, and second, they often measure a spatial phenomenon, such as air pollution or the location of people in a room. Standards for sensor data are therefore developed within the OGC. Since 2011, there has been a usable standard for the Semantic Web, the Semantic Sensor Network (SSN). This standard seems be due some improvement, giving it more possibilities and making it easier to use. The result will have to contribute to more general availability and increased interoperability and usability of sensor data on the web. And that offers opportunities for the Internet of Things (or Web of Things) and making our living environments smarter, for instance.

"The web will become the main place to share data, even more so than it already is now"

Frans Knibbe

Coverage data on the web

Coverage is an important form of spatial data that we need to be able to share easily and accessibly on the web. A coverage is a collection of data that describes a spatially and/or temporally variable phenomenon. A coverage can cover one to four dimensions. Examples of cover data are satellite images, tomograms, time series, and point clouds. It’s a class of data that’s very important for research, for example when researching the environment or climate. The result of the work will probably be a formal ontology for coverage data on the Web, based as much as possible on existing and yet to be developed specifications of the OGC, and possibly on the Data Cube Vocabulary for multidimensional data.

Ambitious. Too Ambitious?

The objectives are very ambitious. If the working group can achieve them, the web will become the main place to share data, even more so than it already is. Even so, the standards and best practices will also be readily deployable on intranets to solve problems with non-sharable data and poorly connected systems within organizations. But are the objectives achievable? Although the group consists of seventy experts in spatiotemporal data and/or web data, the majority participate as volunteers and some problems are very difficult to solve. Time will tell, but there is certainly hope for useful results around the end of 2016.

That is why the working group has decided to take a pragmatic approach by using existing standards and specifications and by working together with other communities. Moreover, the web is a platform that consists of many modules that, when cleverly combined, result in new things. If the working group fails to achieve all the objectives and requirements, its work will, at least, generate building blocks for further development.


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