1. © D. Wong 2002 © D. Wong 2003 1 CS610 / CS710 Database Systems I Daisy Wong

2. © D. Wong 2002 © D. Wong 2003 2 Objectives  Modeling and design of databases.  Programming: queries and DB operations

3. © D. Wong 2002 © D. Wong 2003 3 Database  A large collection of data: –stored in mass storage –exists over a long period of time –Can take on a variety of appearances depending on the requirements at the time –Can serve as the data source for a variety of applications

4. © D. Wong 2002 © D. Wong 2003 4 Database Examples  Examples: –Wal-Mart : records every item purchased in every store –L. L. Bean: records detail information of each customer and their purchases –Hospitals: record patient demographics, conditions and progress, test results, etc –...  This course, refer to a collection of data managed by a Database Management System (DBMS)

5. © D. Wong 2002 © D. Wong 2003 5 DBMS  A combination of software, data, and structure of the data that support: –Users to create databases and specify their schema –Users to query and modify the data –Storage of very large amount of data, secure the data from accident or unauthorized use, and allow efficient access –Control concurrent access from many users, presenting correct data to each user, and prevent accidental corruption of the data from simultaneous accesses

6. © D. Wong 2002 © D. Wong 2003 6 DBMS lingo  Schema –logical structure of the data. Use Data Definition Language (DDL)  Query –A question about the data. Use Data Manipulation Language (DML)  Transaction (or atomic transaction) –A logical unit of work that must be completed as a whole or not at all.

7. © D. Wong 2002 © D. Wong 2003 7 Three levels of database schemas External View1External View2External View3 Logical Schema Disk Internal schema Logical level Internal level External level Logical to external mappings Internal to Logical mappings

8. © D. Wong 2002 © D. Wong 2003 8 DBMS User Roles  End users –access the database for information to do their jobs. Casual (use simple user interfaces) vs. Sophisticated ( use DML)  Database designers –specify information content (use DDL) to create database systems  Application developers –design and develop applications that extend the functionality of the dbms. E.g. user interface, data analysis and data mining, various business services  Database administrators (DBAs) –administer databases: control access, maintain data accuracy and integrity, monitor and improve database performance

9. © D. Wong 2002 © D. Wong 2003 9 A little history  First attempt – file systems  Hierarchical model (tree based)  Network model (graph base)  Relational model –Proposed by E. F. Codd (1970) –Data should be presented to user as tables (relations) –Queries expressed in a very high-level language –SQL (Structured Query Language) – most important language based on relational model

10. © D. Wong 2002 © D. Wong 2003 10 Relational Model  A conceptual model that represents data as relations.  Relations – tables of data  Query using SQL: SELECT balance FROM Accounts WHERE accountNo = 34567;  Relational DBMS finds an efficient way to answer the query accountNonamebalance 12345Sally1000.21 34567Sue285.48 ……… Accounts

11. © D. Wong 2002 © D. Wong 2003 11 Major components of a DBMS (Simplified. Figure 1.1) DDL commands External level Logical level Internal level Transaction Commands Query Manager DDL compiler Transaction Manager Buffer/File Storage Manager Data Metadata Queries/updates DBA Users / applications

12. © D. Wong 2002 © D. Wong 2003 12 Figure 1.1: Database management system components Ref. FCDS 2ed. by Ullman

13. © D. Wong 2002 © D. Wong 2003 13 Storage Manager Obtains the requested information from data storage Modifies the information if requested and re-store Indexes are used (data structures that help us find data items quickly given a part of their value). Advanced data structures such as B-tree are used for efficient access Indexes are part of the data, their description is part of the metadata Consists of 2 components: file manger and buffer manager 1. 1.File manager keeps track of the location of files on disk and obtains the blocks containing the requested data 2. 2.Buffer manager handles main memory. It manages the memory blocks, obtaining disk blocks from the file manager, trying to optimize the access to data

14. © D. Wong 2002 © D. Wong 2003 14 Query Manager  Parse and optimize the query using a query compiler  Execute the resulting query plan (sequence of actions for the DBMS to perform) –Issues a sequence of requests to storage manager for small pieces of data  Return the result to the requester

15. © D. Wong 2002 © D. Wong 2003 15 Transaction Manager  Assure all transactions are executed properly  ACID properties of “proper” execution: –Atomicity : All of the updates of a transaction are successful, or no update take place –Consistency: Each transaction should leave the database in a consistent state –Isolation: Each transaction, when executed concurrently with other transactions, should have the same effect as if it had been executed by itself –Durability: Once a transaction has completed successfully, its changes to the database should be permanent. Even serious failures should not affect the permanence of a transaction.

16. © D. Wong 2002 © D. Wong 2003 16 Techniques to enforce ACID  Locking – granularity of locks is important.  Logging – write a log to nonvolatile storage. Assure durability.  Transaction Commitment – for durability and atomicity, transactions are computed “tentatively”, recorded, but no changes are made to the db until the transaction gets committed. Changes copied to the log, then copied to db.

17. © D. Wong 2002 © D. Wong 2003 17Trends  Object Oriented DB –Richer data types –Classes and class hierarchy enable share or reuse of sw and schemas –Protect misuse through abstract data types  Object Relational DB  Constraints and triggers handling  Multimedia data  Data Integration to support advance data analysis such as data mining. E.g. data warehouses, data marts  Multi-tier Client-Server architecture, move more processing to the client  Parallel processing  Support Web sites

18. © D. Wong 2002 © D. Wong 2003 18 Knowledge Discovery in Databases (KDD) Knowledge Data Target Data Preprocessed Data Transformed Data Patterns Selection Preprocessing Transformation Data Mining Interpretation / Evaluation Reference: Fayyad; Smyth: "From Data Mining to Knowledge Discovery: An Overview" 1996

19. © D. Wong 2002 © D. Wong 2003 19 Ch. 2 Entity-Relationship Data Model  Data models  Entity-Relationship diagrams  Design Principles  Modeling of constraints  Weak entity sets

20. © D. Wong 2002 © D. Wong 2003 20 Data Modeling  Used for conceptual database design Ideas ODL E/R Relational Schema Relational DBMS Object-oriented DBMS Classes / Objects

21. © D. Wong 2002 © D. Wong 2003 21 Data Models Value-OrientedObject-Oriented Examples –Relational –Logic –Object-oriented –Network –Hierarchical Distinct objects by Data values Object identity Redundancy handling Reduced by Design capabilities Use pointers to objects Many-to-many relationships Handled the same Only binary relationships

22. © D. Wong 2002 © D. Wong 2003 22 Relational Model  Based on mathematically defined relations of entities  Consists of: –Attributes (fields) –Domain legitimate values of attributes (data range) –Views of data presented in table format –Create new views by projections of the database –Records are n-tuples, where n = # of attributes

23. © D. Wong 2002 © D. Wong 2003 23 Entity-Relationship (E/R) Diagrams  Represents the schematic of a database  Useful for designing the conceptual model  Entity set : classes of objects  Entity : member of an entity set (data)  Attributes : properties of the entities in an entity set  Relationship – describe how entities relate to each other

24. © D. Wong 2002 © D. Wong 2003 24 Entity-Relationship Diagrams Symbols attributes relationships entity sets Cardinality: one - one many - one m many - many m n

25. © D. Wong 2002 © D. Wong 2003 25 Entity-Relationship Diagrams (continue)  Entity –Has a set of attributes –The key is underlined  Key –Attributes which uniquely identify an entity in an entity set –An inherent property of the data (e.g. movie title and year) –Serve as a constraint SS#