Summary of the Sort Service

Question from: Lee Latimer ljl@blcmp.org.uk Thu, 11 Sep 1997 13:33:30 +0100

Please provide a summary description of the Sort Service.

A Z39.50 Search results in the creation of a result set, maintained at the server, and the client may then "retrieve" records, via the Z39.50 Present service. For example, as a result of a search the server may create a result set of 100 records, and so inform the client, who may then request, say, the first 3 records.

According to the Z39.50 abstract result set model, the records in the result set are not ordered according to any specific scheme (or at least they are not in any predictable order). An annoying consequence is this: suppose, as above where there are 100 records, the client wants the three most recent (i.e. based on 'date of publication'). There is no easy way to find those records, short of retrieving the entire result set.

That's why the Sort service was developed: it allows the client to request that a particular result set be sorted, based on a specific key (e.g. "date of publication", descending). If the server supports the sort service (and also supports sorting on the requested key, in this case "date of publication") then following the Sort, the client may subsequently retrieve the first three records, and they will be the three most recent.

That's a quick summary and it omits most of the details. The sort service is quite a bit more complex than this simplistic description.