Distributed Name Service (DNS) Management Programming Manual

Glossary
46958 Tandem Computers Incorporated Glossary–9
Header token. A special kind of token that provides information pertaining to the SPI
message as a whole. Header tokens are typically common to all or most messages of a
specific kind. They differ from other tokens in several ways: they exist in the buffer at
initialization and their values are usually set by SSINIT; they can occur only once in a
buffer; they are never enclosed in a list; they cannot be moved to another buffer using
SSMOVE; and programs cannot position to them or retrieve their values using the
NEXTCODE or NEXTTOKEN operation. Programs retrieve the values of header
tokens by passing appropriate token codes to SSGET, and can change the values of
some header tokens by passing their token codes to SSPUT. Examples of header
tokens for commands are the command token, the object type token, the maximum-
response token, the server-version token, the maximum-field-version token, and the
checksum token. Examples of header tokens for event messages are the event number,
the event generation time, the logging time, the maximum-field-version token, and the
checksum token.
Header type. A header token in an SPI message that indicates whether the message is a
command, response, or event message.
Information command. A command that retrieves information about an object but does
not act on or change the object. Compare with Action command.
Information token. A response token that conveys information requested by a command,
as opposed to one that serves a syntactical purpose such as delimiting a list, one that
indicates response continuation, one that identifies how a command completed, or one
that identifies an error. Object-selector tokens, attribute tokens, status tokens, and
statistics tokens are kinds of information tokens.
Initial position. The location in an SPI buffer just prior to the first non-header token.
Compare with Current position and Next position.
Initialize. To prepare a data structure to have values assigned to it. For example, the
SPI SSINIT procedure initializes the buffer by building the message header; the
SSNULL procedure initializes an extensible structured token by assigning null values
to the fields of the structure.
Interprocess message. The data one process sends to another with a single file system or
message system call.
List. In an SPI message, a grouping of tokens that defines a context for scanning the
buffer and extracting tokens, using the SSGET procedure. A list construct imposes
hierarchy in the buffer: to retrieve the tokens from a list, the application must first go
to the start of the list, retrieve the initial list token, retrieve tokens from the list, and
then exit the list to the next higher level of tokens by retrieving the end-list token. SPI
defines three kinds of lists: data lists, error lists, and generic lists.
List token. A syntax token that begins a list. SPI defines three different tokens to begin
a list, depending on the type of list: the data-list token, the error-list token, and the
generic-list token. Compare with End-list token; see also Syntax token.
Literal. A symbol that can be used in a TAL program to represent a constant value. The
definition files for use with TAL contain some literals and some pre-defined variables.