Why has deegree webservices 3.2 been dubbed “INSPIRE release”? This blog post series explains why it is an excellent choice for providing compliant INSPIRE Download Services, especially if you want the full monty: Interoperable Direct Access Download Services that serve valid, harmonized datasets.
What is an INSPIRE Download Service anyway?
From a technical perspective, this is best answered by the official Technical Guidance document for INSPIRE Download Services. The current version is 3.0 (published 12/06/2012):
To summarize, this document defines three different classes of INSPIRE Download Services:
- Pre-defined Dataset Download Service based on ATOM
- Pre-defined Dataset Download Service based on WFS
- Direct Access Download Service
Basically, a Pre-defined Dataset Download Service based on ATOM provides service and dataset feeds that ultimately contain download links to the actual datasets. Datasets can only be downloaded in full. There are no filtering capabilities to query subsets.
A Pre-defined Dataset Download Service based on WFS is an OGC Web Feature Service 2.0 that complies to “Simple WFS”, “Query” and “HTTP GET” conformance classes. There’s just a single, mandatory stored query for retrieving full datasets using their identifier. Again, there are no filtering capabilities to query subsets.
A Direct Access Download Service extends a Pre-defined Dataset Download Service based on WFS by additional OGC WFS conformance classes: “Basic WFS”, “Ad hoc Query”, “Resource Identification”, “Minimum Standard Filter”, “Minimum Spatial Filter”, “Minimum Temporal Filter” and “Minimum XPath”.
Although Pre-defined Dataset Download Services may seem much simpler to implement, a Direct Access Download Service has the benefit that is offers filtering possiblities to WFS clients: Not only can you download a full dataset, but also a subset (e.g. the geo objects inside a bounding box). The possibilities for filtering are based on the OGC Filter Encoding 2.0 specification.
deegree WFS (contained in deegree webservices 3.2) allows to set up a Direct Access Download Service without any license fees and similar (or less) implementation complexity. Sounds to good to be true? Read on!
Interoperable vs. non-interoperable Download Services
Besides Pre-defined and Direct Access, INSPIRE guidelines make a distinction between Non-interoperable and Interoperable Download Services:
- Non-interoperable (initial stages): Offered datasets are not required to be compliant
- Interoperable: Offered datasets have to be compliant
Basically, the Non-interoperable phase is meant to reduce the efforts for data providers to meet the INSPIRE requirements. They can just offer their data in existing formats ‘as-is’. However, in the long run, all data offered by INSPIRE Download Services has to be compliant to the corresponding Data Theme Specification. This means that the data provider needs to transform their existing datasets into harmonized datasets that are valid with respect to the corresponding Data Theme Specification.
The following diagram (taken from the Technical Guidance) provides an overview of the milestones on the road to Interoperable Download Services (click for full size):
deegree WFS is suitable both for setting up both Non-interoperable and Interoperable Download Services. It can deal with the INSPIRE Data Model and return valid, harmonized INSPIRE GML datasets. Additionally, deegree’s GML mapping language can be used to perform data harmonization on-the-fly (but you can also perform data harmonization using any other technology).
The next part of this blog post series will discuss what harmonized datasets are exactly and why the deegree WFS implementation stands out for setting up Interoperable Direct Access Download Services.