A GLIDER program uses variables of different types. GLIDER includes definitions for certain types, variables, constants, functions and procedures required for general processing. Others are also system defined to meet special requirements of particular models.
Besides, users may define types, variables, constants, functions and procedures needed to program their models. Other instances of language elements may also be defined: messages, functions given by pairs of values, frequency tables, data base tables, and needed statistics.
All user's variables must be explicitly declared, as mandatory in Pascal.
The names assigned to types, variables, constants, functions and procedures
are called identifiers. They are strings of at most
twelve characters, including letters, numbers and the sign _ . The
first character in the identifier must be a letter. GLIDER is case
insensitive 
,
so Water_Temp and WATER_temp are the same variable.
A declared identifier must not duplicate any system or previously user defined identifier. See Chapter 9 for a list of system defined identifiers.
The declaration section begins with the separator DECL as the first word of a line. Identifiers are declared in the following subsections of the DECL section, according to their element class:
1. TYPE typesA declaration consists of the name of the element class (one of the above) followed by identifier declarations, according to the syntax described in the following sections.2. CONST constants
3. VAR variables
4. NODES nodes
5. MESSAGES messages
6. GFUNCTIONS user's functions defined by values
7. TABLES frequency tables
8. DBTABLES tables from a data based system
9. PROCEDURES user's built procedures and functions
10. STATISTICS required from nodes and variables