what are Package Specifications in plsql?

Answer 1

The package specification contains public declarations. The declared items are accessible from anywhere in the package and to any other subprograms in the same schema. Figure 10-1 illustrates the scoping.

Package Scope

Package Scope
Description of Package Scope"

The spec lists the package resources available to applications. All the information your application must use the resources is in the spec. For example, the following declaration shows that the function named factorial takes one argument of type INTEGER and returns a value of type INTEGER:

FUNCTION factorial (n INTEGER) RETURN INTEGER; -- returns n!

That is all the information needed to invoke the function. You need not consider its underlying implementation (whether it is iterative or recursive for example).

If a spec declares only types, constants, variables, exceptions, and call specifications, the package body is unnecessary. Only subprograms and cursors have an underlying implementation. In Example 10-1, the package needs no body because it declares types, exceptions, and variables, but no subprograms or cursors. Such packages let you define global variables, usable by stored subprograms and triggers, that persist throughout a session.

A Simple Package Specification Without a Body

CREATE PACKAGE trans_data AS  -- bodiless package
   TYPE TimeRec IS RECORD (
      minutes SMALLINT,
      hours   SMALLINT);
   TYPE TransRec IS RECORD (
      category VARCHAR2(10),
      account  INT,
      amount   REAL,
      time_of  TimeRec);
   minimum_balance    CONSTANT REAL := 10.00;
   number_processed   INT;
   insufficient_funds EXCEPTION;
END trans_data;