= FDO RFC 20 - Enhanced Capabilities Support =

This page contains an change request (RFC) for the FDO Open Source project.  
More FDO RFCs can be found on the [wiki:FDORfcs RFCs] page.


== Status == 
 
||RFC Template Version||(1.0)|| 
||Submission Date|| April 30, 2008 ||
||Last Modified|| Greg Boone [[Timestamp]]||
||Author||Greg Boone||
||RFC Status||Draft|| 
||Implementation Status||Pending||
||Proposed Milestone||3.4.0.0||
||Assigned PSC guide(s)||Greg Boone||
||'''Voting History'''||(vote date)||
||+1|| ||
||+0|| ||
||-0|| ||
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== Motivation ==

The objective of this RFC is to propose enahncements to the capability interfaces of the FDO API in order that applications are able to eliminate all special case handling of FDO provider capabilities. It will be necessary to gather feedback from applications such as OSGeo !MapGuide !OpenSource and Autodesk Map 3D to determine that we have a complete set of capabilities implemented in the FDO API and that all special casing can be emininated with the proposed changes outlined in this RFC. 

It is also necessary to introduce a previously discussed concept of !DataStore level capabilities. !DataStore capabilities are a necessity in the FDO API due to the fact that certain providers can only communicate certain capabilities that are !DataStore specific after a fullly formed connection to the provider has been established. There are cases where a provider may support a certain capability, e.g. write or long transactions, whereas a particular datastore for the current connection has limitations. E.g. it may be read only, or it may not support long transactions. Currently, there is no way for a client application to determine these datastore specific restrictions except for a few specific cases around class level capabilities.

Finally to simplify capability handling as the FDO API evolves, we will evaluate the possibilities of introducing an API change that would see the FDO API use constants to identify capabilities supported by its providers. This will make it easier to add new capabilities without changing the API every time a need arises to add a new capability.


== Scenarios ==

Here are some areas where the current level of !DataStore agnostic capabilities are insufficient.

    * The ODBC provider can connect to different sources from Excel files to Access databases to various RDBMS’. However, the capabilities of each source are somewhat different.
    * The Oracle provider can connect to different Oracle versions. With the introduction of Oracle XE there is the case of an Oracle datastore that does not support long transaction versioning or persistent locking.
    * Some providers restrict the type of geometry in a geometry property to a specific type rather than category of types. SHP is a good example of this. The provider may advertise that the geometry can be linear, which implies polyline, multi-polyline, etc. However, when the user enters a multi-polyline geometry, an exception is thrown that it cannot be written. A more fine grained specification of allowed geometry types will avoid these situations.