SNAX/HLS Configuration and Control Manual

The Application Interface
Product Overview
104705 Tandem Computers Incorporated 1–5
Principal Parts of
SNAX/HLS
SNAX/HLS is a comprehensive system of programs that implements the operational
environment. The principal components are:
The SNAX/HLS main module (HLSOBJ), which performs SNA services for
requesting applications.
The Resource Definition language and compiler (HLSRDT), which are used to
define the characteristics of sessions and the application interface that is used.
The HLSCOM module, which provides a command interface for operational
control of SNAX/HLS.
The Application Prototyping and Simulation (APS) process, which allows
interactive SNAX/HLS verb execution. APS facilitates the development of
application prototypes by allowing you to explore many scenarios quickly and by
answering your questions about each scenario.
The SNAX/HLS Trace Analysis Program (HLSTAP), which translates and
displays internal SNAX/HLS traces in an easy-to-understand mnemonic format.
The following subsections present details on each of these components.
The Application
Interface
SNAX/HLS provides a consistent application interface that is independent of the
requester language. This is achieved by providing a set of verbs at the interface to
handle all SNA communication functions requested by the application. This set of
verbs forms the high-level application interface.
Verbs A verb is a formatted message that describes to SNAX/HLS the function to be
performed. The verb consists of a code that specifies the requested operation (for
example, SEND-DATA or CLOSE-SESSION), modifiers, indicators, and, in some cases,
application data. The indicator fields can be either verb requests, (specifying functions
to be performed), or verb modifiers, (changing the action of the verb). To ensure that
SNAX/HLS functions in a Pathway environment, indicators are always byte values,
typically Y or N, and not bit masks.
Replies to Verbs Each verb has a corresponding reply. The verb reply is a formatted message from
SNAX/HLS to the application program, indicating the result or status of the verb
request. Verb replies can also be accompanied by indicator fields and optional data.
Central to the concept of the verb reply is the RETURN-CODE field. The
RETURN-CODE is a generalized mechanism for standard error and status reporting,
much like the mechanism used for condition-code or file-error reporting used in the
Tandem NonStop Kernel.
Delivery of Verbs and
Replies
Because verb execution always involves a two-way message between the application
and SNAX/HLS, the WRITEREAD call is used for message delivery. You can use
SNAX/HLS with any language supported by Tandem because all these languages
support the equivalent of a WRITEREAD.