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NDF Names   

So far, examples of obtaining access to NDF data structures have depended on routines which use parameters and therefore require the support of a programming environment. However, it is also possible to use NDF_ routines in ``standalone'' applications and hence to access NDF structures whose location within the underlying data system (HDS) is specified explicitly, i.e. by name.

The name of an NDF dataset normally consists of up to three parts, as follows:[*]

      <file_name><hds_path><subscripts>

Here, <file_name> is the name of the HDS ``container file'' which holds the data, <hds_path> is the HDS ``path'' which identifies the location of the HDS object (i.e. the NDF) within the container file, and <subscripts> is a parenthesised set of subscripts which may be used to select a section from the NDF (see §[*]). The container file name is always required, but the other two components are optional. Thus, a simple NDF name might look like:

      mydatafile

(if the NDF were the top-level object in the container file, which is often the case), while a fairly complicated NDF name might resemble:

      /users/bill/datafiles/today.RUN(66).BAND_B(1:66,1.04)

Here, the first `.' separates the HDS path from the file name. Names of this sort may be supplied by users of NDF_ applications in response to prompts issued via a programming environment.

However, when NDF names are specified explicitly within applications, an alternative naming possibility exists because HDS files contain hierarchies of data structures rather similar to the directory structure of computer filing systems (see SUN/92 for a description of HDS data structures). Therefore, just as you can specify a file using an absolute name or a name relative to the current directory, so you can also specify the location of an NDF data structure within an HDS container file in an absolute or a relative fashion.

To give an absolute NDF name, you would specify it in full, as in the examples above,[*] while to give a relative NDF name, you would supply an active HDS locator and the name of the NDF data structure relative to the HDS object that the locator identifies.

To allow this, most NDF_ routines that handle the names of NDFs will accept two arguments: an HDS locator and an associated character string containing a name. The following section illustrates how these are used.



next up previous
Next: Finding and Importing NDFs
Up: CONNECTING WITH THE DATA SYSTEM
Previous: CONNECTING WITH THE DATA SYSTEM


Starlink User Note 33
R.F. Warren-Smith
11th January 2000
E-mail:rfws@star.rl.ac.uk

Copyright © 2000 Council for the Central Laboratory of the Research Councils