1. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Chapter 1 Introduction: Databases and Database Users Modified by Dr. Hsiang-Fu Yu National Taipei University of Education 2011 for 6 th Edition

2. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 2 Outline Types of Databases and Database Applications Basic Definitions Typical DBMS Functionality Example of a Database (UNIVERSITY) Main Characteristics of the Database Approach Database Users Advantages of Using the Database Approach A Brief History of Database Applications When Not to Use Databases

3. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 3 Types of Databases and Database Applications Traditional Applications Numeric and Textual Databases More Recent Applications Multimedia Databases Geographic Information Systems (GIS) Data Warehouses and OnLine Analytical Processing (OLAP) systems Real-time and Active Databases Many other applications

4. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 4 Basic Definitions Database A collection of related data. Represents some aspect of the real world. Logically coherent collection of data with inherent meaning. Built for a specific purpose. Data Known facts that can be recorded and have an implicit meaning. Mini-world or universe of discourse (UoD) Some part of the real world about which data is stored in a database. For example, student grades and transcripts at a university.

5. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 5 Basic Definitions (cont.) Database Management System (DBMS) A software package/system to facilitate the creation and maintenance of a computerized database. Database System The DBMS software together with the data itself. Sometimes, the applications are also included.

6. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 6 Simplified database system environment

7. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 7 Typical DBMS Features Defining a database Specify the data types, structures, and constraints of the data to be stored. Meta-data Database definition or descriptive information. Stored by the DBMS in the form of a database catalog or dictionary. Manipulating a database Query and update the database. Generate reports. Sharing a database Allow multiple users and programs to access the database simultaneously.

8. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 8 Typical DBMS Features (cont.) Application program Accesses database by sending queries to DBMS. Query Causes some data to be retrieved. Transaction May cause some data to be read and some data to be written into the database. Protection System protection Security protection

9. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 9 Typical DBMS Features (cont.) Maintain the database system Allow the system to evolve as requirements change over time. Maintain the database and associated programs over the lifetime of the database application.

10. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 10 Example of a Database (with a Conceptual Data Model) Mini-world for the example: Part of a UNIVERSITY environment. Data records (some mini-world entities): STUDENTs COURSEs SECTIONs (of COURSEs) GRADE_REPORT PREREQUISITE

11. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 11

12. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 12 Example of a Database (cont.) Phases for designing a database: Requirements specification and analysis Conceptual design Logical design Physical design Construct UNIVERSITY database Store data to represent each student, course, section, grade report, and prerequisite as a record in appropriate file. Relationships among the records

13. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 13 Example of a Database (cont.) Manipulation involves querying and updating Examples of queries: Retrieve the transcript. List the names of students who took the section of the ‘Database’ course offered in fall 2008 and their grades in that section. List the prerequisites of the ‘Database’ course. Examples of updates: Change the class of ‘Smith’ to sophomore. Create a new section for the ‘Database’ course for this semester. Enter a grade of ‘A’ for ‘Smith’ in the ‘Database’ section of last semester.

14. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 14 Main Characteristics of the Database Approach Self-describing nature of a database system Insulation between programs and data, and data abstraction Support of multiple views of the data Sharing of data and multi-user transaction processing

15. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 15 Self-describing Nature of a Database System Database system contains complete definition of structure and constraints. A DBMS catalog stores the description of a particular database (e.g. data structures, types, and constraints). The description is called meta-data, describing structure of the database. This allows the DBMS software to work with different database applications. The database catalog used by:  DBMS software  Database users who need information about database structure

16. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 16 Insulation between Programs and Data Program-data independence Structure of data files is stored in DBMS catalog separately from access programs. Program-operation independence Operations (or methods for object class) specified in two parts: Interface includes operation name and data types of its arguments. Implementation can be changed without affecting the interface. The application programs can operate on the data by invoking the operations through their names and arguments, regardless of how the operations are implemented.

17. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 17 Example of a Simplified Database Catalog

18. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 18 Data Abstraction The characteristic that allows program-data independence and program-operation independence Conceptual representation of data Does not include details of how data is stored or how operations are implemented Data model Type of data abstraction used to provide conceptual representation To hide storage details and present the users with a conceptual view of the database Programs refer to the data model constructs rather than data storage details.

19. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 19 Support of Multiple Views of the Data Each user may see a different view of the database, which describes only the data of interest to that user. View Subset of the database Contains virtual data derived from the database files but is not explicitly stored Multi-user DBMS Users have a variety of distinct applications. Must provide facilities for defining multiple views.

20. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 20 Sharing of Data and Multi-user Transaction Processing Allow multiple users to access the database at the same time. Concurrency control software Ensure that several users trying to update the same data do so in a controlled manner Result of the updates is correct OnLine Transaction Processing (OLTP) is a major part of database applications. This allows hundreds of concurrent transactions to execute per second.

21. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 21 Sharing of Data and Multi-user Transaction Processing (cont.) A Transaction is An execution program or process that includes one or more database accesses, such as reading or updating. Supposed to execute a logically correct database access if executed in its entirety without interference from other transactions. A DBMS must enforce following transaction properties Isolation Each transaction appears to execute in isolation from other transactions. Atomicity Either all the database operations in a transaction are executed or none are.

22. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 22 Sharing of Data and Multi-user Transaction Processing (cont.) Concurrency control within the DBMS guarantees that each transaction is correctly executed or aborted. Recovery subsystem ensures each completed transaction has its effect permanently recorded in the database.

23. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 23 Database Users Users may be divided into Those who actually use and control the database content, and those who design, develop and maintain database applications (called “Actors on the Scene”), and Those who design and develop the DBMS software and related tools, and the computer systems operators (called “Workers Behind the Scene”).

24. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 24 Actors on the Scene Database Administrators Authorizing access to the database Coordinating and monitoring its use Acquiring software and hardware resources Monitoring efficiency of operations Database Designers Define the content, the structure, the constraints, and functions or transactions against the database. Communicate with the end-users and understand their needs.

25. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 25 Actors on the Scene (cont.) End-users People whose jobs require access to the database types Casual: access database occasionally when needed Naive or Parametric: they make up a large section of the end-user population. They use previously well-defined functions in the form of “canned transactions” against the database. Examples are bank-tellers or reservation clerks who do this activity for an entire shift of operations.

26. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 26 Types of End-users (cont.) Sophisticated: These include business analysts, scientists, engineers, others thoroughly familiar with the system capabilities. Many use tools in the form of software packages that work closely with the stored database. Stand-alone: Mostly maintain personal databases using ready-to-use packaged applications. An example is a tax program user that creates its own internal database. Another example is a user that maintains an address book

27. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 27 Actors on the Scene (cont.) System Analysts Determine requirements of end users. Application Programmers (Software Engineers) Implement these specifications as programs.

28. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 28 Workers behind the Scene DBMS System Designers and Implementers Design and implement the DBMS modules and interfaces as a software package. Tool Developers Design and implement tools – the software packages that facilitate database modeling and design, database system design, and improved performance. Operators and Maintenance Personnel Responsible for the actual running and maintenance of the hardware and software environment for the database system

29. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 29 Advantages of Using the DBMS Approach Controlling redundancy Redundancy leads to Duplication effort Wasted storage spaces Inconsistency Data normalization Denormalization Sometimes necessary to use controlled redundancy to improve the performance of queries Restricting unauthorized access to data Security and authorization subsystem Privileged software

30. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 30 Advantages of Using the DBMS Approach (cont.) Providing persistent storage for program objects Complex object in C++ can be stored permanently in an object-oriented DBMS. To avoid the impedance mismatch problem in object-oriented DBMS The data structures provided by the DBMS are incompatible with the programming language’s data structures.

31. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 31 Advantages of Using the DBMS Approach (cont.) Providing storage structures and search techniques for efficient query processing Indexes Buffering and caching Query processing and optimization Providing backup and recovery services Providing multiple user interfaces Representing complex relationships among data

32. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 32 Advantages of Using the DBMS Approach (cont.) Enforcing integrity constraints on the database Integrity Constraints 保持資料對人而言在語意上正確 Referential integrity constraint Every section record must be related to a course record Key or uniqueness constraint Every course record must have a unique value for Course_number Business rules Inherent rules of the data model

33. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 33 Advantages of Using the DBMS Approach (cont.) Permitting inferencing and actions using rules Deductive database systems Provide capabilities for defining deduction rules. Inference new information from the stored database facts. Trigger Rule activated by updates to the table Stored procedures More involved procedures to enforce rules

34. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 34 Additional Implications of Using the DBMS Approach Potential for enforcing standards This is very crucial for the success of database applications in large organizations. Standards refer to data item names, display formats, screens, report structures, meta-data (description of data), Web page layouts, etc. Reduced application development time Incremental time to add each new application is reduced.

35. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 35 Additional Implications of Using the Database Approach (continued) Flexibility to change data structures Database structure may evolve as new requirements are defined. Availability of current information Extremely important for on-line transaction systems such as airline, hotel, car reservations. Economies of scale Wasteful overlap of resources and personnel can be avoided by consolidating data and applications across departments.

36. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 36 A Brief History of Database Applications Early Database Applications The Hierarchical and Network Models were introduced in mid 1960s and dominated during the seventies. A bulk of the worldwide database processing still occurs using these models, particularly, the hierarchical model. Providing data abstraction and application flexibility with relational databases Relational model was originally introduced in 1970, was heavily researched and experimented within IBM Research and several universities. Relational DBMS Products emerged in the early 1980s. Separate physical storage of data from its conceptual representation. Provide a mathematical foundation for data representation and querying.

37. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 37 A Brief History of Database Applications (cont.) Object-oriented applications and the need for more complex databases Object-Oriented Database Management Systems (OODBMSs) were introduced in late 1980s and early 1990s to cater to the need of complex data processing in CAD and other applications. Their use has not taken off much. Used in specialized applications: engineering design, multimedia publishing, and manufacturing systems. Many relational DBMSs have incorporated object database concepts, leading to a new category called object-relational DBMSs (ORDBMSs)

38. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 38 A Brief History of Database Applications (cont.) Interchanging data on the Web for e-commerce using XML Extended markup language (XML) primary standard for interchanging data among various types of databases and Web pages Extending database capabilities for new applications Extensions to better support specialized requirements for applications Enterprise resource planning (ERP) Customer relationship management (CRM) Databases versus information retrieval Information retrieval (IR) Deals with books, manuscripts, and various forms of library- based articles

39. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 39 Database vs. File-processing Traditional file processing Each user defines and implements the files needed for a specific software applications as part of programming the application. Database approach Single repository maintains data that is defined once and then accessed by various users.

40. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 40 When not to use a DBMS Main overhead costs of using a DBMS High initial investment and possible need for additional hardware. The generality that a DBMS provides for defining and processing data Overhead for providing security, concurrency control, recovery, and integrity functions.

41. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 41 When not to use a DBMS (cont.) A DBMS may be unnecessary when Simple, well-defined database applications not expected to change at all Stringent, real-time requirements that may not be met because of DBMS overhead Embedded systems with limited storage capacity No multiple-user access to data When no DBMS may suffice If the database system is not able to handle the complexity of data because of modeling limitations If the database users need special operations not supported by the DBMS.

42. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 42 Summary Types of Databases and Database Applications Basic Definitions Typical DBMS Functionality Example of a Database (UNIVERSITY) Main Characteristics of the Database Approach Database Users Advantages of Using the Database Approach When Not to Use Databases