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Context Tables

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TableDecl = "'table'" Ident "(" Ident ":" Ident{ "," Ident ":" Ident} ")" .

A declaration of the form

  • 'table' T ( F1 : Tn , ... , Fn : Tn )
introduces a context table T.

A context table is an unbounded collection of entries. An entry has a unique key and a record of fields. These fields have names F1, ..., Fn and types T1, ..., Tn. The name of the table, T, acts as the name for the type of the keys.

A unique key is created by a key definition statement. The value of a field is defined by a context update and accessed in a context query.

   
Example

'table' Label (Coordinate: INT)
This defines a table Label. Entries of this table have one field with name Coordinate and type INT. Keys of entries have type Label.

A value of type Label can be created without knowing the value of field Coordinate.


Lab :: Label
defines Lab as unique value of type Label.

Lab'Coordinate <- Loc
may be used later to define the field Coordinate.

Lab'Coordinate -> Loc
is used to access the field Coordinate.





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