Variable-Length Records Variable-length records arise in database systems in several ways: Storage of multiple record types in a file. Record types that allow variable lengths for one or more fields such as strings(varchar) Record types that allow repeating fields (used in some older data models). Attributes are stored in order Variable length attributes represented by fixed size (offset,length),with actual data stored after all fixed length attributes Null values represented by null-value bitmap Null bitmap (stored in 1 byte) 0000 21,5 26,10 36,10 65000 10101 Srinivasan Comp.Sci. Bytes 0 4 8 12 2021 26 36 45 Database System Concepts-7th Edition 13.7 @Silberschatz,Korth and SudarshanDatabase System Concepts - 7 13.7 ©Silberschatz, Korth and Sudarshan th Edition Variable-Length Records ▪ Variable-length records arise in database systems in several ways: • Storage of multiple record types in a file. • Record types that allow variable lengths for one or more fields such as strings (varchar) • Record types that allow repeating fields (used in some older data models). ▪ Attributes are stored in order ▪ Variable length attributes represented by fixed size (offset, length), with actual data stored after all fixed length attributes ▪ Null values represented by null-value bitmap