Description of VTL Operators

The structure used for the description of the VTL-DL Operators is made of the following parts:

• Operator name, which is also used to invoke the operator

• Semantics: a brief description of the purpose of the operator

• Syntax: the syntax of the Operator (this part follows the conventions described in the previous section “Conventions for describing the operators’ syntax”)

• Syntax description: detailed explanation of the meaning of the various parts of the syntax

• Parameters: list of the input parameters and their types

• Constraints: additional constraints that are not specified with the meta-syntax and need a textual explanation

• Semantic specifications: detailed description of the semantics of the operator

• Examples: examples of invocation of the operator

The structure used for the description of the VTL-ML Operators is made of the following parts:

• Operator name, followed by the operator symbol (keyword) which is used to invoke the operator

• Syntax: the syntax of the Operator (this part follows the conventions described in the previous section “Conventions for describing the operators’ syntax”)

• Input parameters: list of all input parameters and the subexpressions with their meaning and the indication if they are mandatory or optional

• Examples of valid syntaxes: examples of syntactically valid invocations of the Operator

• Semantics for scalar operations: the behaviour of the Operator on scalar operands, which is the basic behaviour of the Operator

• Input parameters type: the formal description of the type of the input parameters (this part follows the conventions described in the previous section “Description of the data types of operands and results”)

• Result type: the formal description of the type of the result (this part follows the conventions described in the previous section “Description of the data types of operands and results”)

• Additional constraints: additional constraints that are not specified with the meta-syntax and need a textual explanation, including both possible semantic constraints under which the operation is possible or impossible, and syntactical constraint for the invocation of the Operator

• Behaviour: description of the behaviour of the Operator for non-scalar operations (for example operations at Data Set or at Component level). When the Operator belongs to a class of Operators having a common behaviour, the common behaviour is described once for all in a section of the chapter “Typical behaviours of the ML Operators” and therefore this part describes only the specific aspect of the behaviour and contains a reference to the section where the common part of the behaviour is described.

• Examples: a series of examples of invocation and application of the operator in case of operations at Data Sets or at Component level.