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Field Descriptors

A Tuple could be implemented as
  • a list of field descriptors for a record instance
    (where a FieldDesc gives (offset,length,type) information)
  • along with a reference to the Record data 

typedef struct {
  ushort    nfields;   // number of fields/attrs
  ushort    data_off;  // offset in struct for data
  FieldDesc fields[];  // field descriptions
  Record    data;      // pointer to record in buffer
} Tuple;

Fields are derived from relation descriptor + record instance data.