1. Chapter 9 Database Systems Introduction to CS 1 st Semester, 2014 Sanghyun Park

2. Outline  Database Fundamentals  Data Models  Relational Model  Object-Oriented Databases(skip)  Maintaining Database Integrity  Traditional File Structures  Data Mining(skip)  Social Impact of Database Technology(skip)

3. Database Fundamentals  A database is a collection of data that is ________, not necessarily physically, _________  A database management system (_______) defines, creates, and maintains a database  The DBMS also allows users _________ access to data in the database relying on schemas and subschemas  A ________ is a description of the entire database structure used by the DBMS  A __________ is a description of only that portion of the database ________ to a particular user’s needs  Databases have evolved as a means of _________ data storage systems

4. File vs. Database Organization (1/2)  _________ data  ___________ problem

5. File vs. Database Organization (2/2)

6. Layered Approach to Database Implementation  A typical database system consists of ____ layers – an _________ layer and a database management layer  Advantages of this dichotomy  Allows for the construction and use of _________ tools  Provides a means for controlling access to the databases  Achieves data _____________

7. Database Models  A database model defines the _______ design of data  The model also describes the ____________ between different parts of data  In the history of database design, three models have been in use:  Hierarchical model  Network model  Relational model

8. Hierarchical Model  Data are organized as a ____  Each entity has only ___ parent but can have several children

9. Network Model  Entities are organized in a _____, where some entities can be accessed through _______ paths  There is __ hierarchy

10. Relational Model (1/2)  Data are organized in two-dimensional ______ called _________  There is no hierarchical or network structure imposed on the data

11. Relational Model (2/2)  Each column in a relation is called an _________  The total number of attributes for a relation is called the ______ of the relation  Each row in a relation is called a _____  The total number of rows in a relation is called the __________ of the relation  The cardinality of a relation changes when tuples are added or deleted; this makes the database _________

12. Issues of Relational Design (1/4)  Lack of efficiency due to __________  Possibility of information ____ when deleting a tuple  The source of the problems is that we have combined more than one concept into a ______ relation

13. Issues of Relational Design (2/4)

14. Issues of Relational Design (3/4) ASSIGNMENT relation Job Id Start DateTerm Date S25X F5 S25Z 3-1-1999 10-1-2001 5-1-2001 4-30-2001 * *  This database contains information about employees in EMPLOYEE relation, about available jobs in JOB relation, and about job history in ASSIGNMENT relation  Additional information is implicitly available by ________ the information from _________ relations

15. Issues of Relational Design (4/4)  Finding the department in which employee 23Y34 has worked

16. Relational Operations: SELECT

17. Relational Operations: PROJECT

18. Relational Operations: JOIN (1/3)

19. Relational Operations: JOIN (2/3)

20. Relational Operations: JOIN (3/3)

21. Issues of Implementation  The data in a database are actually stored in a ____ storage system  A DBMS allows the application software to be written in terms of a ______________  It is the duty of the ______ to accept commands in terms of the relational _____ and convert them into actions relative to the actual storage structure  The simplest way for a DBMS to implement a relation is to store it as a __________ file  To provide rapid access to entries, the DBMS would store the relation as an _______ file or utilize ________ techniques

22. Structured Query Language (1/2)  The language called ____ (Structured Query Language) is used extensively by application software programmers for manipulating databases  A query involving a combination of SELECT, PROJECT, and JOIN operations can be expressed as a _____ SQL statement  We should read a SQL statement as a description of the information ______ rather than a _________ of activities to be performed  not procedural but __________

23. Structured Query Language (2/2)  SELECT statement selectEMPLOYEE.Name, ASSIGNMENT.StartDate fromEMPLOYEE, ASSIGNMENT whereEMPLOYEE.EmplId = ASSIGNMENT.EmplId  INSERT statement insertinto EMPLOYEE values(‘42Z12’, ‘Sue A. Burt’, ‘33 Fair St.’, ‘444661111’)  DELETE statement deletefrom EMPLOYEE whereName = ‘G. Jerry Smith’  UPDATE statement updateEMPLOYEE setAddress = ‘1812 Napoleon Ave.’ whereName = ‘Joe E. Baker’

24. Maintaining Database Integrity (1/2)  ___________ is a sequence of operations that must all happen together (e.g., money transfer between accounts)  Before a transaction is allowed to alter the database, the alteration to be performed is first recorded in the ___  The point at which all the steps in a transaction have been recorded in the log is called the ____________  At this point DBMS becomes ________ to the transaction  If problems arise before a transaction has reached its commit point, the log can be used to _______ (undo) the activities actually performed by the transaction

25. Maintaining Database Integrity (2/2)  Simultaneous access problems  Incorrect summary problem  Lost update problem  ______ is used for preventing others from accessing data being used by a transaction  Shared lock is used when ________ data  Exclusive lock is used when _________ data

26. Traditional File Structures  A ___ is an external collection of related data treated as a unit  The primary purpose of a file is to _____ data  Files are stored in what are known as ________ or _________ storage devices such as disk and tape  For our purposes, a file is a collection of data _______ with each record consisting of one or more _____  The _____ method determines how records can be retrieved: sequentially or randomly

27. Taxonomy of File Structures

28. Sequential Files While Not EOF { Read the next record Process the record }

29. Applications of Sequential Files  The sequential file is used in applications that need to access ___ records from beginning to end  For example, if personal information about each employee is stored in a file, we can use sequential access to retrieve each record at the end of the month to print the paychecks  The sequential file is not efficient for _______ access

30. Indexed Files  To access a record in a file randomly, we need to know the _______ of the record  An indexed file is made of a data file, which is a sequential file, and an _____  The index itself is a very ____ file with only two fields: the ___ of the sequential file and the ________ of the corresponding record on the disk

31. Mapping in an Index File

32. Logical View of an Indexed File

33. Hashed Files  In an indexed file, the index _____ the key to the address; A hashed file uses a ________ to accomplish this mapping  The hashed file eliminates the need for an ____ file (index)  However, we will see that hashed files have their own problems

34. Modulo Division Hashing Method

35. Collision (1/2)  The population of keys is greater than the ______ of records in the data file  Because there are many keys for each address in the file, there is a possibility that more than one key will hash to the _____ address in the file  We call the set of keys that hash to the same address ________  A _______ is the event that occurs when a hashing algorithm produces an address for an insertion key, and that address is already occupied

36. Collision (2/2)

37. Collision Resolution: Open Addressing

38. Collision Resolution: Linked List Resolution

39. Collision Resolution: Bucket Hashing