The DECLARE_VARIABLE clause lets you declare a host language
    variable by referring to a field associated with a database
    relation. The variable inherits the data type and size
    attributes associated with the field. See the BASED ON clause
    for information on declaring program functions: Pascal TYPE(s),
    and C typedef(s).

    The DECLARE_VARIABLE and DEFINE_TYPE clauses have exactly the
    same function. Oracle Rdb decided to rename the clause to clarify
    that its function is to declare host language variables, not to
    define host language types. Note that the DEFINE_TYPE clause
    may still be used; however, Rdb recommends that all new
    applications use the DECLARE_VARIABLE clause in place of the
    DEFINE_TYPE clause.