[xquery-talk] How do different XQuery products implement modules?

[Oliver Hallam]

This is the behaviour of XQSharp:

> 1. Is the module URI just an arbitrary character string, or does it 
> have any
> semantics?

The value of the module URI is used only as a namespace.

>   1a. In particular, is it the location of a resource on the web?

If it is, that is irrelevant.  Could be used for library documentation.

> 2. Do you allow several different modules in the same query to have 
> the same
> module URI?

Yes.

>   2a. if so, can different "import module" declarations import different
> subsets of these?

Each "import module" statement can import a subset of the modules in a 
library
allowing access to those functions imported.  Checking for XQST0034 and 
XQST0036
is performed for each query and only takes into account the modules 
imported.

> 3. Can users import a module without specifying a location URI? If so, 
> how
> is the module located?

The static context allows for a set of location hints to be provided for 
any
given module namespace.  These hints are used alongside any given in the 
query,
so if no hints are given, then the hints given in the static context are 
used.

> 4. If import module specifies a location URI, is it used, and if so how?

The URI is resolved, and the source of the module is retrived from that 
location.

> 5. If import module specifies more than one location URI, how are they 
> used?

Each location hint specifies the location of a module and all the 
modules are
imported as in the answer to question 4.

>   5b. If multiple location URIs are allowed, what happens if
>   import module specifies the same location URI more than once?

The location hints are treated as a set - that is, any repeated URIs are 
ignored

> 6. What happens when two modules A and B both import module URI M
>
>   6a. specifying the same location URI

The module is resolved once, and its functions and global variables are 
added to
the set available to A and B.

>   6b. specifying different location URIs

Each location URI is loaded as a separate module, and A and B can only 
use the
subset of the module they imported.  Conflict resolution is only 
performed on a
per-module basis, so it is possible for A and B to refer to different 
functions
in M with the same name.  This allows for modules to be built against 
different
versions of the same library (which may or may not be a good thing).

>   6c. without specifying a location URI

Since the location hints in the static context are added to all library 
imports,
the sections of the library defined by these modules are accessible to 
every
module that imports that namespace

> 7. Is it possible (by means of multiple imports) to create two different
> "instances" of the same module in a query, with distinct values of global
> variables, or do all imports get the same instance with a common set of
> variables?

All global variables and functions are global to the query.  Global 
variables are
uniquely identified by their name and the location hint of the module 
that defined
them.
If we were to perform the XPST0034 checking on a per library basis, then 
a global
variable would be uniquely identified by its name.

Oliver Hallam
XQSharp.com