Chapter 1: Introduction to Databases and Database Users PDF

Chapter 1 Introduction: Databases and Database Users Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Outline ◼ File based versus database based approach to data management. ◼ Types of Databases and Database Applications ◼ Basic Definitions ◼ Typical DBMS Functionality ◼ Exam...

Chapter 1 Introduction: Databases and Database Users Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Outline ◼ File based versus database based approach to data management. ◼ 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 Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 2 Drawbacks of using file systems to store data ◼ Data redundancy and inconsistency ◼ Multiple file formats, duplication of information in different files ◼ Difficulty in accessing data ◼ Need to write a new program to carry out each new task ◼ Data isolation ◼ Multiple files and formats ◼ Integrity problems ◼ Integrity constraints (e.g., account balance > 0) become “buried” in program code rather than being stated explicitly ◼ Hard to add new constraints or change existing ones Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Types of Databases and Database Applications ◼ Traditional Applications: ◼ Numeric and Textual Databases ◼ More Recent Applications: ◼ Multimedia Databases ◼ Geographic Information Systems (GIS) ◼ Data Warehouses ◼ Real-time and Active Databases ◼ Many other applications ◼ First part of book focuses on traditional applications ◼ A number of recent applications are described later in the book (for example, Chapters 24,26,28,29,30) Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 4 ◼ It is fair to say that Database systems play critical role in almost all areas where computers are used including: ◼ Database Applications: ◼ Banking: transactions ◼ Airlines: reservations, schedules ◼ Universities: registration, grades ◼ Sales: customers, products, purchases ◼ Online retailers: order tracking, customized recommendations ◼ Manufacturing: production, inventory, orders, supply chain ◼ Human resources: employee records, salaries, tax deductions ◼ Databases can be very large. ◼ Databases touch all aspects of our lives Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 5 Basic Definitions ◼ Database: ◼ A collection of logically related data. ◼ Data: ◼ Known facts that can be recorded and have an implicit meaning. ◼ Information : processed data ◼ Mini-world: ◼ Some part of the real world about which data is stored in a database. For example, student grades and transcripts at a university. ◼ Database represents some aspects of the mini world. ◼ Any changes in the mini world are reflected in the database. ◼ 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. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 6 Simplified database system environment Alter table student add address char (200) not null ; Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 7 Example of a simplified database catalog Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 8 Typical DBMS Functionality ◼ Define a particular database in terms of its data types, structures, and constraints ◼ Construct or Load the initial database contents on a secondary storage medium ◼ Manipulating the database: ◼ Retrieval: Querying, generating reports ◼ Modification: Insertions, deletions and updates to its content ◼ Accessing the database through Web applications ◼ Processing and Sharing by a set of concurrent users and application programs – yet, keeping all data valid and consistent Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 9 Example of a Database (with a Conceptual Data Model) ◼ Mini-world for the example: ◼ Part of a UNIVERSITY environment. ◼ Some mini-world entities: ◼ STUDENTs ◼ COURSEs ◼ SECTIONs (of COURSEs) ◼ (academic) DEPARTMENTs ◼ INSTRUCTORs Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 10 Example of a Database (with a Conceptual Data Model) ◼ Some mini-world relationships: ◼ SECTIONs are of specific COURSEs ◼ STUDENTs take SECTIONs ◼ COURSEs have prerequisite COURSEs ◼ INSTRUCTORs teach SECTIONs ◼ COURSEs are offered by DEPARTMENTs ◼ STUDENTs major in DEPARTMENTs ◼ Note: The above entities and relationships are typically expressed in a conceptual data model, such as the ENTITY-RELATIONSHIP data model (see Chapters 3, 4) Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 11 Example of a simple database Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 12 Main Characteristics of the Database Approach ◼ Self-describing nature of a database system: ◼ A DBMS catalog stores the description of a particular database (e.g. data structures, types, and constraints) ◼ The description is called meta-data. ◼ This allows the DBMS software to work with different database applications. ◼ Insulation between programs and data: ◼ Called program-data independence. ◼ Allows changing data structures and storage organization without having to change the DBMS access programs. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 13 Main Characteristics of the Database Approach (continued) ◼ Data Abstraction: A data model is used 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 ◼ 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. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 14 Main Characteristics of the Database Approach (continued) ◼ Sharing of data and multi-user transaction processing: ◼ Allowing a set of concurrent users to retrieve from and to update the database. ◼ 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 ◼ OLTP (Online Transaction Processing) is a major part of database applications. This allows hundreds of concurrent transactions to execute per second. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 15 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”). Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 16 Database Users ◼ Actors on the scene ◼ Database administrators: ◼ Responsible for authorizing access to the database, for coordinating and monitoring its use, acquiring software and hardware resources, controlling its use and monitoring efficiency of operations. ◼ Database Designers: ◼ Responsible to define the content, the structure, the constraints, and functions or transactions against the database. They must communicate with the end-users and understand their needs. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 17 Categories of End-users ◼ Actors on the scene (continued) ◼ End-users: They use the data for queries, reports and some of them update the database content. End-users can be categorized into: ◼ Casual: access database occasionally when needed ◼ Naïve 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. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 18 Categories of End-users (continued) ◼ 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 Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 19 Advantages of Using the Database Approach ◼ Controlling redundancy in data storage and in development and maintenance efforts. ◼ Sharing of data among multiple users. ◼ Restricting unauthorized access to data. ◼ Providing persistent storage for program Objects ◼ In Object-oriented DBMSs – see Chapters 20-22 ◼ Providing Storage Structures (e.g. indexes) for efficient Query Processing Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 20 Advantages of Using the Database Approach (continued) ◼ Providing backup and recovery services. ◼ Providing multiple interfaces to different classes of users. ◼ Representing complex relationships among data. ◼ Enforcing integrity constraints on the database. ◼ Drawing inferences and actions from the stored data using deductive and active rules Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 21 Additional Implications of Using the Database 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. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 22 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. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 23 When not to use a DBMS ◼ Main inhibitors (costs) of using a DBMS: ◼ High initial investment and possible need for additional hardware. ◼ Overhead for providing generality, security, concurrency control, recovery, and integrity functions. ◼ When a DBMS may be unnecessary: ◼ If the database and applications are simple, well defined, and not expected to change. ◼ If there are stringent real-time requirements that may not be met because of DBMS overhead. ◼ If access to data by multiple users is not required. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 24 When not to use a DBMS ◼ 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. Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 25 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 Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 1- 26