Section 5.2.3.1. Program features

Star_Base is a fully functional STAR File parser and may be used to test the syntactic validity of an input STAR File. It may be used to write an input STAR File directly to the output stream, while validating the structural integrity as the contents are parsed. The input format and comments are discarded on output.

Given a valid input file, Star_Base guarantees to write output in fully compliant STAR format.

If a data name is supplied as a request item, Star_Base will return the single or multiple values associated with that data name and their associated context according to the principles of Section 5.2.2, i.e. all loop structures, data-block headers and global headers will be returned, and save frames will be expanded as required to accommodate de-referencing of frame codes as returned values.

Where multiple data items are requested, Star_Base will write their occurrences to its output stream in the order they were requested, not in the order of appearance in the input file. This may disturb data relationships that are implicit in the ordering or association of values in the input file, but it is the responsibility of the user to track and retain such associations where they are an essential part of an application-level data model. As emphasized before, a generic STAR tool will make no assumptions about data models and will simply return values and contexts as requested.

To illustrate the effect of this, consider a request for the following data items from the example file of Fig. 5.2.2.1:Star_Base will return the following result:

However, if the same items are requested in a different order, the result is structured differently:

In the examples so far, one or more data items have been requested by name. Star_Base extends the type of requests that can be made through its own query language. This gives it much of the power of a database query language such as SQL. Three types of query are supported, known as data, conditional and branching requests.

A data request is a straightforward generalization of the request by data name. Individual data items may be requested by name, as may individual data blocks or save frames. Wild carding is permitted to generalize the requests. More details are given in Section 5.2.3.2.

A conditional request involves one or more conditions; only data items satisfying the conditions are returned. More details are given in Section 5.2.3.3.

A branching request applies similar conditions to establish the context in which matching data items occur within the file, but may also apply scoping rules to select among the available contexts. Only data items matching both the conditions imposed on their values and the requested scope are returned. It is the existence of such branching conditions that gives Star_Base the ability to select data matching the specific requirements of overlying data models. Again, however, it is emphasized that the program itself operates without any semantic awareness of the significance of the data that is implied within the overlaid data model. More details on branching requests are given in Section 5.2.3.4.