10 Notes

Here's a collection of information that might be important to specific servers but is hard to fit into a general tutorial.

• It's possible to replace the three separate programs, one for the DAS, DDS and DataDDS, with a single program. Clearly there all share close to 90% of the same code. You can tell which object is being requested by either using the old Unix trick of making the programs symbolic links to a single executable and then checking to see which name was used to invoke it, or by modifying the dispatch script slightly to pass that information along with the other parameters.
• Similarly, you can subclass the DAS and DDS objects adding methods to them to build up the attributes and variables instead of writing functions to do that task.
• For complex data sets, it's likely that you'll need to create some new fields in the data type classes you specialized.
• If you're writing a server that will principally be for internal use, or you expect many many small accesses, you should look into using the Java software or implementing your server as an Apache module. Contact support or the dods-tech email list for help with the latter.
• You can get help from the OPeNDAP Home page, the opendap-tech email list and the OPeNDAP user support desk.
• The OPeNDAP Project has developed two tools to help with serving datasets that contain many files. The first is to set up a `file server' a kind of catalog of URLs that is itself a OPeNDAP data set. The second is called the Aggregation Server (AS). The AS can automatically aggregate discrete datasets, accessed as either as files (in some cases) or URLs to produce a single data set. See the OPeNDAP Home page and/or contact User Support for help with this.
• When you're returning error messages, be sure to trim file pathnames so that the real path to data is hidden.
• If you have a data set and its API requires you to store a lot of state information that's not specific to a given variable or data type, consider creating a mixin class and making your data type children inherit from it in addition to the DAP classes. Because the `virtual contractors' are used to create instances of the data type classes, you can be sure that in your server, all instances of Byte, etc., contain the mixin. Use the dynamic_cast operator to access the mixin's methods.