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11.2.2.2.1 “Unlimited” resources available
This is quite an unlikely situation where the resources are not a limitation while compaction is. This would be the case in a hi-end aircraft equipped with state of the art
installation. In this case, EXI combining schema knowledge and post compression would be the best options, for though being very consuming in time and resources; it provides
the best performances in terms of compactness.
11.2.2.2.2 Limited resources available: between Client and DMS
In this situation, EXI with post compression is an interesting choice; it offers excellent compaction performances and if one is not concerned by the time needed for the
information to be relayed, but is looking at equipment with limited resources, EXI Document appears as the best solution.
11.2.2.3 Strong resources constraints
In the case where the resources are the most critical feature of the information exchange Crisis cell …. One could simply go for GZip compression. It is widely used, very easy
to set up and can offer interesting compression performance and reasonable costs in terms of CPU time and memory. Fast Infoset is also an excellent choice in this situation
11.2.3 Recommended Approach
During the Session negotiation, the DMS shall propose, among the different module options, the possibility for the client to select compression options for the future
exchange between DMS and client. The set of options defined by the client as a response shall constitute the compression policy. The client shall be able to select different options
based on different criteria e.g. a specific type of compression for a specific type of data, plus a general compression for all other type of data. This way the client will be able to
tune its policy for each of the different approach it could have resources constraint, time constraint, compaction constraint.
For this reason, the DMS shall offer the following compression method to the client: Fast Infoset with or without post compression
For finer treatment of compression based on the nature of the data, the DMS should also offer the following compression methods:
GZip EXI with or without post compression, with or without schema knowledge
The DMS stores the compression policy requested by the client it shall potentially be able to provide it on request. Whenever the DMS receives data for the client, it shall
perform a check based on data type to assess if and which compression is needed. The data is then compressed and sent to the client.
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11.2.4 Implementation
During OWS-9, the first plan is to be able to demonstrate the interest of compression on the one hand and also to demonstrate the capability of the DMS to segregate the traffic
and apply compression only in certain situations. To achieve this purpose, only one compression algorithm is needed. We will then have two different behaviors
compressing or not compressing on the DMS or client side. Based on this, we can demonstrate the capability of the DMS of having different behavior depending on the
compression policy, defined at the session negotiation, which can apply on:
The data link used The types of data
In the implementation of the DMS web service, which will likely be done with Apache, the plan is to implement Fast Infoset for the following reasons:
Ease of use : as demonstrated in [OGC 11-097], Fast Infoset is relatively easy to set up
Feasibility: Fast Infoset binary serialization is already present on the Apache Axis 2 implementation
11.2.5 Performance Measures
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