Physical Database Design

1. Physical Database Design University of California, Berkeley School of Information Management and Systems SIMS 257: Database Management SIMS 257: Database Management

2. Review • Normalization • Denormalization SIMS 257: Database Management

3. Normalization Unnormalized Relations First normal form Functional dependencyof nonkey attributes on the primary key - Atomic values only Second normal form No transitive dependency between nonkey attributes Third normal form Boyce- Codd and Higher Full Functional dependencyof nonkey attributes on the primary key All determinants are candidate keys - Single multivalued dependency SIMS 257: Database Management

4. Normalization • Normalization is performed to reduce or eliminate Insertion, Deletion or Update anomalies. • However, a completely normalized database may not be the most efficient or effective implementation. • “Denormalization” is sometimes used to improve efficiency. SIMS 257: Database Management

5. Physical Database Design Access Methods Indexes Today Based on McFadden Modern Database Management and Atre Database:Structured Techniques for Design, Performance and Management SIMS 257: Database Management

6. Database Design Process Application 1 Application 2 Application 3 Application 4 External Model External Model External Model External Model Application 1 Conceptual requirements Application 2 Conceptual requirements Conceptual Model Logical Model Internal Model Application 3 Conceptual requirements Application 4 Physical Design Conceptual requirements SIMS 257: Database Management

7. Physical Database Design • Many physical database design decisions are implicit in the technology adopted • Also, organizations may have standards or an “information architecture” that specifies operating systems, DBMS, and data access languages -- thus constraining the range of possible physical implementations. • We will be concerned with some of the possible physical implementation issues SIMS 257: Database Management

8. Physical Database Design • The primary goal of physical database design is data processing efficiency • We will concentrate on choices often available to optimize performance of database services • Physical Database Design requires information gathered during earlier stages of the design process SIMS 257: Database Management

9. Physical Design Information • Information needed for physical file and database design includes: • Normalized relations plus size estimates for them • Definitions of each attribute • Descriptions of where and when data are used • entered, retrieved, deleted, updated, and how often • Expectations and requirements for response time, and data security, backup, recovery, retention and integrity • Descriptions of the technologies used to implement the database SIMS 257: Database Management

10. Physical Design Decisions • There are several critical decisions that will affect the integrity and performance of the system. • Storage Format • Physical record composition • Data arrangement • Indexes • Query optimization and performance tuning SIMS 257: Database Management

11. Storage Format • Choosing the storage format of each field (attribute). The DBMS provides some set of data types that can be used for the physical storage of fields in the database • Data Type (format) is chosen to minimize storage space and maximize data integrity SIMS 257: Database Management

12. Objectives of data type selection • Minimize storage space • Represent all possible values • Improve data integrity • Support all data manipulations • The correct data type should, in minimal space, represent every possible value (but eliminated illegal values) for the associated attribute and can support the required data manipulations (e.g. numerical or string operations) SIMS 257: Database Management

13. Access Data Types • Numeric (1, 2, 4, 8 bytes, fixed or float) • Text (255 max) • Memo (64000 max) • Date/Time (8 bytes) • Currency (8 bytes, 15 digits + 4 digits decimal) • Autonumber (4 bytes) • Yes/No (1 bit) • OLE (limited only by disk space) • Hyperlinks (up to 64000 chars) SIMS 257: Database Management

14. Access Numeric types • Byte • Stores numbers from 0 to 255 (no fractions). 1 byte • Integer • Stores numbers from –32,768 to 32,767 (no fractions) 2 bytes • Long Integer(Default) • Stores numbers from –2,147,483,648 to 2,147,483,647 (no fractions). 4 bytes • Single • Stores numbers from -3.402823E38 to –1.401298E–45 for negative values and from 1.401298E–45 to 3.402823E38 for positive values. 4 bytes • Double • Stores numbers from –1.79769313486231E308 to –4.94065645841247E–324 for negative values and from 1.79769313486231E308 to 4.94065645841247E–324 for positive values. 15 8 bytes • Replication ID • Globally unique identifier (GUID) N/A 16 bytes SIMS 257: Database Management

15. Controlling Data Integrity • Default values • Range control • Null value control • Referential integrity • Handling missing data SIMS 257: Database Management

16. Designing Physical Records • A physical record is a group of fields stored in adjacent memory locations and retrieved together as a unit • Fixed Length and variable fields • Denormalization SIMS 257: Database Management

17. Denormalization • Usually driven by the need to improve query speed • Query speed is improved at the expense of more complex or problematic DML (Data manipulation language) for updates, deletions and insertions. SIMS 257: Database Management

18. Customer ID Address Name Telephone Order Order No Date Taken Date Dispatched Date Invoiced Cust ID Order Order No Date Taken Date Dispatched Date Invoiced Cust ID Cust Name Customer ID Address Name Telephone Downward Denormalization Before: After: SIMS 257: Database Management

19. Order Order No Date Taken Date Dispatched Date Invoiced Cust ID Cust Name Order Order No Date Taken Date Dispatched Date Invoiced Cust ID Cust Name Order Price Order Item Order No Item No Item Price Num Ordered Order Item Order No Item No Item Price Num Ordered Upward Denormalization SIMS 257: Database Management

20. Designing Physical Files • Overview • terminology • Access methods SIMS 257: Database Management

21. DBMS External Model Internal Model Access Methods Physical Design • Internal Model/Physical Model User request Interface 1 Interface 2 Operating System Access Methods Interface 3 Data Base SIMS 257: Database Management

22. Physical Design • Interface 1: User request to the DBMS. The user presents a query, the DBMS determines which physical DBs are needed to resolve the query • Interface 2: The DBMS uses an internal model access method to access the data stored in a logical database. • Interface 3: The internal model access methods and OS access methods access the physical records of the database. SIMS 257: Database Management

23. Physical File Design • A Physical file is a portion of secondary storage (disk space) allocated for the purpose of storing physical records • Pointers - a field of data that can be used to locate a related field or record of data • Access Methods - An operating system algorithm for storing and locating data in secondary storage • Pages - The amount of data read or written in one disk input or output operation SIMS 257: Database Management

24. Internal Model Access Methods • Many types of access methods: • Physical Sequential • Indexed Sequential • Indexed Random • Inverted • Direct • Hashed • Differences in • Access Efficiency • Storage Efficiency SIMS 257: Database Management

25. Physical Sequential • Key values of the physical records are in logical sequence • Main use is for “dump” and “restore” • Access method may be used for storage as well as retrieval • Storage Efficiency is near 100% • Access Efficiency is poor SIMS 257: Database Management

26. Indexed Sequential • Key values of the physical records are in logical sequence • Access method may be used for storage and retrieval • Index of key values is maintained with entries for the highest key values per block(s) • Access Efficiency depends on the levels of index, storage allocated for index, number of database records, and amount of overflow • Storage Efficiency depends on size of index and volatility of database SIMS 257: Database Management

27. Adams Becker Dumpling Actual Value Address Block Number Dumpling Harty Texaci ... 1 2 3 … Getta Harty Mobile Sunoci Texaci Index Sequential Data File Block 1 Block 2 Block 3 SIMS 257: Database Management

28. Key Value Address Key Value Key Value Key Value Address Address Address 785 805 536 678 150 385 385 678 805 3 4 5 6 7 8 9 … 1 2 Indexed Sequential: Two Levels 001 003 . . 150 251 . . 385 455 480 . . 536 605 610 . . 678 705 710 . . 785 791 . . 805 SIMS 257: Database Management

29. Indexed Random • Key values of the physical records are not necessarily in logical sequence • Index may be stored and accessed with Indexed Sequential Access Method • Index has an entry for every data base record. These are in ascending order. The index keys are in logical sequence. Database records are not necessarily in ascending sequence. • Access method may be used for storage and retrieval SIMS 257: Database Management

30. Indexed Random Becker Harty Actual Value Address Block Number Adams Becker Dumpling Getta Harty 2 1 3 2 1 Adams Getta Dumpling SIMS 257: Database Management

31. Btree F | | P | | Z | B | | D | | F | H | | L | | P | R | | S | | Z | Devils Hawkeyes Hoosiers Minors Panthers Seminoles Aces Boilers Cars Flyers SIMS 257: Database Management

32. Inverted • Key values of the physical records are not necessarily in logical sequence • Access Method is better used for retrieval • An index for every field to be inverted may be built • Access efficiency depends on number of database records, levels of index, and storage allocated for index SIMS 257: Database Management

33. Student name Course Number CH 145 101, 103,104 Adams Becker Dumpling Getta Harty Mobile Actual Value Address Block Number CH 145 CS 201 CS 623 PH 345 1 2 3 … CS 201 102 CS 623 105, 106 Inverted CH145 cs201 ch145 ch145 cs623 cs623 SIMS 257: Database Management

34. Direct • Key values of the physical records are not necessarily in logical sequence • There is a one-to-one correspondence between a record key and the physical address of the record • May be used for storage and retrieval • Access efficiency always 1 • Storage efficiency depends on density of keys • No duplicate keys permitted SIMS 257: Database Management

35. Hashing • Key values of the physical records are not necessarily in logical sequence • Many key values may share the same physical address (block) • May be used for storage and retrieval • Access efficiency depends on distribution of keys, algorithm for key transformation and space allocated • Storage efficiency depends on distibution of keys and algorithm used for key transformation SIMS 257: Database Management

36. Comparative Access Methods Factor Storage space Sequential retrieval on primary key Random Retr. Multiple Key Retr. Deleting records Adding records Updating records Sequential No wasted space Very fast Impractical Possible but needs a full scan can create wasted space requires rewriting file usually requires rewriting file Indexed No wasted space for data but extra space for index Moderately Fast Moderately Fast Very fast with multiple indexes OK if dynamic OK if dynamic Easy but requires Maintenance of indexes Hashed more space needed for addition and deletion of records after initial load Impractical Very fast Not possible very easy very easy very easy SIMS 257: Database Management