IBM Enterprise Console manual FETCH Statement, ATTR=,$TYPE,VALUE=,4, 1$TYPE=4

SELECT statements and their associated clauses are evaluated in the order they appear in the CDS file. If all the clauses of a SELECT statement are evaluated successfully, the incoming event matches the corresponding class.

After an event is matched with a class because of successful SELECT statement evaluation, processing continues with the FETCH statement, unless the class is *DISCARD*, in which case the event is discarded. If the evaluation of a SELECT statement fails, the kernel tries to match the event with the SELECT statement of the next class. If the incoming event cannot be matched with any class, it is discarded.

Each time a SELECT statement is evaluated successfully, the adapter kernel layer creates three temporary pseudo-variables: $Nn, $Kn, $Vn (where n is the identification number of a clause in the SELECT statement). These variables contain the name, key, and value of the attribute specified in the clause, respectively. The pseudo-variables can then be used in any following SELECT, FETCH, or MAP statement.

By default, the attribute name specified in an ATTR() expression is a string, and the attribute matching this name is searched for sequentially in the incoming event. For most adapters, every incoming event contains a minimum set of mandatory fields. For this reason, each adapter supports built-in keywords that can be used to reference these mandatory attributes and thereby directly access their values. These keywords have the format $attribute_name. Examples of keywords supported by the SNMP adapter are: $AGENT_ADDRESS, $COMMUNITY, $ENTERPRISE, $TYPE, and $SPECIFIC. These keywords refer to the mandatory fields of an SNMP Trap-PDU. Each adapter can also define global variables, such as RECEPTION TIME, SVARBIND, and so forth.

Using the $ notation, a clause for SNMP authentication failure traps can be written as follows:

1: ATTR(=,$TYPE),VALUE(=,4);

This notation is not simpler than the format shown in the previous example, ATTR(=, ″type″), but evaluation will be faster since it results in direct access to the variable instead of a linear search.

The syntax shown in the preceding example is generic, and as such, it can be rather verbose for commonly used criteria. Several shortcuts are provided in order to alleviate the notation. For example, the previous example can be written as follows:

1:$TYPE=4;

Output from the class selection process is the name of the event class, a table of pseudo-variables $Nn, $Kn, $Vn, and all adapter-specific variables (for example, $TYPE, $VARBIND, and so forth).

FETCH Statement

The FETCH statement of a class definition statement allows manipulation and modification to the attribute names, keys, and values retrieved by the SELECT statement for the incoming event. Sometimes it is necessary to perform tasks such as extracting a substring from an attribute value, adding two values, and so forth.

158IBM Tivoli Enterprise Console: Adapters Guide