Packages themselves are never directly invoked or executed. Instead, the constructs contained within the package are invoked. For example, procedures and functions within the package are executed. Other constructs in the package, such as constants and other declared constructs, can be referenced from within other PL/SQL programs, in the same manner that those program units could refer to their own locally declared PL/SQL program constructs.
Referencing Packaged Constructs
To call upon any construct of a package, simply use the package name as a prefix to the construct name. For example, to reference a procedure with no parameters called increase_wages that is stored in a package called hr, use this reference:
hr.increase_wages;
All packaged constructs are invoked in the same fashion: by including the package name as a prefix, with a period separating the package name and the construct name. This notation is often referred to as dot notation. It’s the same format used to refer to database objects that are owned by a schema.
For example, if you have a package called assumptions that defines a public constant called tax_rate, you could use it this way in an expression:
v_full_price := v_pre_tax * (1 + assumptions.tax_rate);
Dot notation is required for references to any packaged constructs from outside of the package. However, although references to constructs from within the same package will accept dot notation, they do not require it.
Using Packaged Constructs
For the purpose of reviewing the rules of using packaged constructs, let’s consider all constructs to be in either of two categories: packaged program units, meaning procedures and functions, and global constructs, meaning packaged variables, constants, cursors, exceptions, and types.
Packaged Program Units
The same rules apply to the use of packaged procedures and functions that apply to stand-alone procedures and functions. In other words, packaged procedures must be called from a single statement, whereas packaged functions must be called from within an expression, just like stand-alone PL/SQL stored functions. Parameters may be passed by positional notation or by named notation.
For example, the following PL/SQL block executes a packaged procedure:
BEGIN
  pack_finance.proc_reconcile_invoice(p_status => ‘ACTIVE’);
END;
Packaged Global Constructs
Packaged global constructs generally behave the same as their locally defined counterparts, with one dramatic difference: Their declaration is global to the user sessions.
Consider the following code sample:
PACKAGE rates AS
  bonus NUMBER(3,2);
END rates;