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https://github.com/OPENDAP/libdap4

A new version of libdap that contains both DAP2 and DAP4 support
https://github.com/OPENDAP/libdap4

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A new version of libdap that contains both DAP2 and DAP4 support

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README 

        
Notes for the prototype AIS implementation:



Note that this code was removed from libdap 3.8.x



------------------------------------------------------------------------------



Current for version 3.7.6 (12 March 2007)



How to use the AIS. These notes correspond to the prototype AIS developed in

March 2003. This version of the AIS works for DAS objects only.



The AIS uses a configuration file which holds the mappings between a primary

data source (aka a DODS server) and one or more AIS resources. The

configuration file to use is named in the .dodsrc file using the AIS_DATABASE

property.



The AIS configuration file is described by src/dap/ais_database.dtd. A short

file looks like:



    

    



    



    

    

    

    



    

    

    

    



    



Each entry must have one  element and may have one or more

 elements. The  elements are applied in the order they

are listed. The 'rule' attribute of  determines how each AIS

resource is combined with the primary resource. By default, attributes in the

AIS resource are combined so that they overwrite existing attributes. If

there's no conflict, the new attribute is added. This applies to containers

as well as single attributes. The replace rule causes the AIS resource

attributes to completely replace those of the primary resource. If the

fallback rule is specified, the AIS resource's attributes are used only if

the primary resource has *no* attributes.



How to use the AIS: 



Keep in mind that this is a prototype and is far, far from

'feature-complete.'



There are two ways to use the AIS right now. First you can use geturl's new

-A option. This option tells geturl that when it gets a DAS object, it should

merge into that object any AIS resources listed for the URL in the current

AIS database (found in the .dodsrc file).



Second you can program with the AIS. The class AISConnect can be used as a

replacement for Connect. This class subclasses Connect and adds the capacity

to use the AIS subsystem I've built. The AIS itself is contained in the

classes AISMerge, AISDatabaseParser and AISResources.



*****************************************************************************



Here are some notes I made while I wrote the code:



* AISConnect does not implement clones for Connect's deprecated methods.

  Should it? Maybe it's time to let those go...



* What happens when the same primary (data) source is listed more than once

  in the database?



* What about primary sources that are regular expressions? Right now lookup

  is ln(N) where N is the number of entries. Regexps make this linear in N.

  Bummer. I can use two databases, et c. but it gets messy very fast. So are

  wild cards important (it doesn't have to be regexps, those are just really

  easy to implement...)?



* I've changed the meaning of 'fallback' so that it works for a whole group

  of attributes rather than each individual attribute. My guess is that this

  will be really unpopular. But it was easy to code and I'm not convinced

  that fallback resources really make that much sense in practice.



* I think that for client-side AIS stuff, the code should be able to read

  from a remote XML file to get the database. Not hard to code. But I wonder

  how useful it would be? It might be cool because a client could get the

  benefit of a remote server but do all the work locally. That would

  'distribute the AIS processing/network load.'



* How will we handle multiple AIS databases? I think this could be really

  important. I like the AIS-in-the-configuration-file less and less, until I

  think about trying to get people to buy into enveloped URLs...



* Is the database file simple enough for people to write by hand? (and one

  look and you can see why we're going to need wildcards... imagine 20K

  URLs).



* I still need to write a bunch more tests.



* I need to hack some code to do the AIS-in-the-URL thing. I figured out how

  to handle that without doing the entire ex pr parse on the client, at least

  for the DAS version ... haven't thought about the DDS & DataDDS much.



* I need to code some serious integration tests. Most of the AIS-specific

  code has unit tests (except for AISConnect, which is barely different from

  the AISMerge Test unit tests).