## 5 Discussion of the Integration Approach
### Potential and Future Work  
Although promising, algebraic solutions are still rare in the Semantic Web and they lack support in the context of geospatial web applications. This results in some difficulties, such as (1) missing tool support for input and output data management for the web; (2) rare examples that illustrate the combined use of logic-based and algebraic specifications for knowledge engineering; and (3) disconnectivity between the algebraic specification and the Semantic Web community. Research in this direction should be extended in order to avoid focusing solely on logic-based efforts towards a Semantic Sensor Web and running the risk of stagnation. Still, it should be kept in mind that also the presented approach has its formal drawbacks. For example, concept disjointness cannot be represented; behavior specified at type class (ADT) level might not be implements, or it might be overwritten. [PERSON] _at al._[41] provide more details about these and other shortcomings, especially in relation to web service matchmaking; most can be generalized.  
The presented work lays the function for further investigations. For example others already suggests using Haskell for common error modeling and elegant propagation [49], but further examinations are required in this field, especially exploiting the interplay between the \"quality\" of VGI and of classical measurements.  
Another open issue is the investigation of place. Our approach currently assumes that geospatial components are introduced in form of geographic locations, with precise geometric attributes. VGI however, might merely include vague place names instead of precise locations, introducing uncertainty on the geographical side. The interplay between place and location should be considered as a major aspect to improve the suggested integration approach.  
The presented algebra does also not explicitly account for (spatio-temporal) level of detail, _i.e._, scale. Here lies a major area for future work, because different information sources are often captured on diverse scales. A functional approach eases scale changes, but more practical examples have to be explored. We expect challenges mostly related to location (_i.e._, geographic scale), because we usually have precise sensor time stamps (scale seconds) available and larger time windows for environmental phenomena. In the case of forest fires, it is usually days. The temporal scale becomes an issue when integrating more than one type of phenomena, which is another direction to be investigated.  
As an improvement that would be easier to achieve, some of the operators used to calculate domain specific functionality, such as value filtering, clustering and the calculation of co-occurrence might be provided more generically as part of an extended observation systems ontology. Common algorithms might be provided as defaults for further re-use. For example, the function that calculates the spatial and temporal co-occurrence of forest fires could be lifted for calculating co-occurrences of any observation result.  
On a more technical level, the interplay with current standard web services of the geospatial and particularly of the Sensor Web community could be established. Data exchange from and to OGC services would be a logical next step. Since the SSN ontology was built using OGC's Observationsand Measurement standard, all required information for the exchange data model are available, _i.e._, it is just a matter of implementing the connectors.