COMP102: Introduction to Databases, 1 & 2

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1 COMP102: Introduction to Databases, 1 & 2 Dr Muhammad Sulaiman Khan Department of Computer Science University of Liverpool U.K. 31/1 Jan/Feb, 2011

2 Introduction

3 The Lecturer: Name: M S Khan Office: G22 Ashton Building Phone: mskhan@liverpool.ac.uk Office hours: arrange by

4 Administrative details: Lectures: Mondays, 12:00 13:00, (NICH-LT) Tuesdays, 10:00 11:00, (NICH-LT) Fridays, 14:00 15:00, (NICH-LT) Place: NL Nicholson Lecture Theatre in Nicholson Building Lab/Practicals (1h/week) Monday, 10:00 11:00 Thursday, 14:00 15:00 Friday, 12:00 13:00, 15:00 16:00 Place: Lab 3, George Holt Building Assessment: Written examination, 80 % Continuous, 4 tasks, 20 %

5 The webpage for this module: khan/comp102.html - go to COMP102, Resources/Sessions login password: your MWS password announcements lecture notes resources

6 Teaching and learning approach: Lectures: on Mondays, Tuesdays and Fridays. Labs/practicals: one hour per week. Assignments/practicals: 4 assessed tasks, written answers/solutions due... Submit your hand-written solutions at the Student s office (Ashton Building).

7 Books for this module: Connolly and Begg, Database Solutions, (10 copies in Harold Cohen Library) Garcia-Molina, Ullman, Widom, Database Systems: The Complete Book, (10 copies in Harold Cohen Library)

8 Introduction to Databases Goals The goals of this module are: To establish an understanding of Information (database) Systems; To encourage the appropriate and efficient design and usage of Database Systems; To provide insight into the design process and social implications of Database Systems; To enable the use of Database Systems in a programming environment.

9 Introduction to Databases Learning Outcomes The learning outcomes of this module are: Gain a basic understanding of the design, operation and usage of database systems; Gain hands-on experience of configuring and using a basic database system; Understand the processes and legal implications of creating and maintaining datbase systems.

10 Introduction to Information and Database Systems Specific topics for today: Data versus Information Information Systems Database Database Management System (DBMS) Functions of a DBMS Advantages and disadvantages of DBMSs

11 Data versus Information Data: A sequence of symbols (digital objects) maintained in a form that can be manipulated by humans or computers. By itself data has no meaning. It must be interpreted and processed by an agent to become Information. Example: Data: 1207 Information: the year when the city of Liverpool was born Data: H 2 SO 4 Information: chemical symbol of a molecule of Sulfuric acid

12 Information Systems Information System: The resources that enable the collection, management, control, and dissemination of data/information throughout an organization. Remark: An information system enables also the transformation of the data into information. It also provides the infrastructure to facilitate the dissemination of information to those who make the decisions crucial to the success of an organization. Example: Examples of information systems: Management Information System: An organized assembly of resources and procedures required to collect, process, and distribute data for use in decision making. Geographic Information System: An information system dealing with spatially referenced data for solving complex planning and management problems.

13 Functions of an Information System Functions of an information system have been basically given in its definition: 1 Acquisition/collection of information. 2 Storage of information. 3 Manipulation/processing of information. 4 Dissemination of information. Remark: Functions 1 and 4 are application specific, i.e., they depend on the specific requirements/structure of an organization that uses the information system. Functions 2 and 3 are usually realized in form of a Database maintained in a Database Management System.

14 Database and Database systems Database: A shared collection of logically related data and metadata (i.e., a description of the data), designed to meet the information needs of an organization. Database Management System (DBMS): A software system that enables users to define, create, and maintain the database and also provides controlled access to this database. Application Program: A computer program that interacts with the database in some way. Database System: A collection of application programs along with the DBMS and the database itself.

15 Example: Examples of database systems: Purchases from the supermarket: The checkout person scans a barcode of each of the goods. An application program which uses the barcodes to find the prices in a database. The program reduces the number of such goods in stock. If the stock low the program places an order for that good. Purchases with a credit card (CC): Online check if sufficient credit left on the card. An application program uses CC number, contacts a CC database, checks if credit limit not exceeded. The application program checks if CC is on the list of stolen CCs. If purchase confirmed, the program updates the credit limit.

16 Example: Examples of database systems, cntd.: Renting a video: A video rental company has a database with video titles it stocks. The database holds the number of copies of each title, info if a copy is on loan, data of the renters, which videos they currently rent and dates they are returned. The database may keep info on videos, e.g., its director, actors. The company can use this info to monitor stock usage, predict future buying trends based on the past rental data. Using the Internet: Many Internet web sites are driven by database applications. Book database at Amazon.com allows browsing books in different categories, by author, title, etc. Database: info on book details, availability, shipping info, stocks. Book details: authors, titles, ISBNs, prices, publishers, reviews. Books can be cross-referenced: listed under several categories, allowing for infos on books usually ordered along with others.

17 Example: A table in the database (StayHome) of video rental company: Another table contains the names of video directors identified by directorno, and yet another names of actors and another info on where they star.

18 These examples cover only very few application domains of database systems. I m sure you are able to find plenty of other examples. Thus: Database systems are very important to our day-to-day life activities. Usually we take these applications for granted, but behind them lies some highly complex technology. Database is at the center of this technology. For the system to support the applications end-users desire in an efficient manner, it requires a well-structured database. Producing this structure is known as database design and is the main goal of this module.

19 Let s be a bit more precise... Database: A shared collection of logically related data and metadata (i.e., a description of the data), designed to meet the information needs of an organization. Shared collection: can be used simultaneously by many departments and users. Logically related: comprises the important objects and the relationships between these objects. Description of the data: the system catalog (metadata) provides description of data to enable data independence. Metadata: data about data, known as system catalog or data dictionary. Data independence: if new data structures added or existing structures modified, then the application programs unaffected (if they don t depend upon what has been modified).

20 Let s be a bit more precise... cntd. Database Management System (DBMS): A software system that enables users to define, create, and maintain the database and also provides controlled access to this database. Application Program: A computer program that interacts with the database by issuing an appropriate request (typically an SQL statement) to the DBMS. DBMS interacts with the users, application programs, and the database. DBMS allows the users to insert, update, delete, and retrieve data from the database. DBMS provides a general inquiry facility to the data, called a query language. SQL (The Structured Query Language): This is the main query language for ralational DBMSs, like Microsoft Access, Microsoft SQL Server, and Oracle.

21 Example: Simple SQL query and data independence in StayHome DB. Consider an SQL query: SELECT catalogno, title FROM Video WHERE (dailyrental 4.00).

22 Example: Simple SQL query and data independence in StayHome DB. Consider an SQL query: SELECT catalogno, title FROM Video WHERE (dailyrental 4.00). Result: (781132, Shrek), (445624, Men in Black II).

23 Example: Simple SQL query and data independence in StayHome DB. Consider an SQL query: SELECT catalogno, title FROM Video WHERE (dailyrental 4.00). Result: (781132, Shrek), (445624, Men in Black II). Now: adding a new column censorinfo with the film censor s office info does not affect the query, but removing column title does.

24 Users interact with the database via application programs (AP) that are used to maintain the database and to generate information. Below the Stock and Sales Departments use their APs to handle data entries, data maintenance and generation of reports all through the DBMS. The physical structure and storage of the data are managed by the DBMS:

25 Views From a point of view of a single end user usually the database system and the data as a whole are too complex, as she only needs a part of it. DBMS provides a view mechanism. View: A virtual table that does not necessarily exist in the database but is generated by the DBMS from the underlying base tables whenever it s accessed. It is essentially some subset of the database and allows each user to have his or her own view of the database. Usually defined as a query that operates on the base tables to produce another virtual table.

26 Benefits of views Provide a level of security: can be set up to exclude data, e.g., about salaries, that some users should not see. Provide a mechanism to customize the appearance of the database. Present a consistent, unchanging picture of the structure of the database, even if the underlying database is changed.

27 Components of DBMS Environment Hardware: Can range from a PC, mainframe, to a network of computers. Software: DBMS, operating system, network software (if necessary) and the application programs. Data: Used by the organization and a description of this data called the schema (meta-data). Procedures: Instructions and rules that should be applied to the design and use of the database and DBMS (e.g., how to log on, how to back-up). People: Includes database designers, database administrators (DBAs), application programmers, and end-users.

28 DBMS architectures Two-Tier Client-Server architecture. Three-Tier Client-Server architecture.

29 Two-Tier Client-Server architecture Client (program) manages main business and data processing logic and user interface. Server (program) manages and controls access to database.

30 Example: A simplified example of the two-tier architecture of StayHome video rental DBMS:

31 Three-Tier Client-Server architecture Client side presented two problems preventing true scalability: Fat client, requiring considerable resources on client s computer to run effectively. Significant client side administration overhead. By 1995, three layers proposed, each potentially running on a different platform. User interface layer runs on client. Business logic and data processing layer middle tier runs on a server (application server). DBMS stores data required by the middle tier. This tier may be on a separate server (database server).

32 Three-Tier Client-Server architecture Advantages: Thin client, requiring less expensive hardware. Application maintenance centralized (at the application server). Easier to modify or replace one tier without affecting others. Separating business logic from database functions makes it easier to implement load balancing. E.g., a transaction processing monitor (TPM) can be used to reduce the number of connections to the database server. TPM: a program that controls data transfer between clients and servers, e.g., similar queries can be collected and executed in batches. Maps quite naturally to Web environment. Web browser plays the role of the thin client. Web server acts as the application server.

33 Example: A simplified example of the three-tier architecture of StayHome video rental DBMS:

34 Functions of a DBMS Data Storage, Retrieval, and Update. Internal physical implementation details (file organization, storage structures) should be hidden from the user. A User-Accessible Catalog (description of the database structure, users, applications). Typical catalog stores: names, types, and sizes of data items; integrity constraints on the data (i.e., constraints that ensure data accuracy); names of authorized users who have access to the data. Transaction Support: Ensures ACID: Atomicity, Consistency, Isolation, Durability. Concurrency Control Services. Recovery Services. Authorization Services: Protect against unauthorized access (security).

35 Functions of a DBMS (cntd.) Support for Data Communication: Usually users access a DBMS server by PCs over a network. Integrity Services: Refer to the correctness and consistency of the stored data. Usually expressed in terms of constraints. Example: For StayHome, say, we impose that any user be allowed to rent at most 10 videos at the same time. Services to Promote Data Independence. Related to the view mechanism. It is easier to ensure physical data independence, e.g., to change the file organization without affecting the views. Logical data independence is more difficult to achieve. Utility Services: Support for the database administrator to maintain the database (e.g., facilities to monitor the database usage). Note: The list of the functions of a DBMS may vary from a system to system. However, modern, large multi-user DBMSs are very complex and provide all of those funcions and more.

36 Transactions Transaction: An action, or series of actions, performed by a user or application program, which accesses or changes the content of the database. Atomicity: Transaction should either be executed as a whole or not at all, e.g., in case of computer crash, the original (consistent) state of the database must be ratained (recovery services). Consistency: Each database has consistency constraints (expectations about relationships among data, e.g., account balance may not be negative). Isolation: Each transaction must appear to be excuted as if no other transaction is executing at the same time. Durability: The effect on the database of a transaction must never be lost, once the transaction has completed.

37 Example: Transactions in the StayHome video rental DBMS. Transactions: add a new staff member to the database, update the salary of a staff member, delete a staff member. More complicated transaction: delete a manager from the database and reassign that branch that she managed to another staff member. In that case more than one change to the database is required. In case of, e.g., power loss during this transaction, consistency can be violated: the branch is not allocated a new manager. Thus, changes that have been made will have to be undone! Mechanism ensuring atomicity is needed.

38 Concurrency Control Services If two users simultaneously only read data, then they do not interfere with each other. In case they simultaneously read and write (update) data, then that can result in inconsistencies. Example: Loss of T2 s update avoided by preventing T1 from reading balx until after update.

39 Database Design: The methodology to develop database systems: Logical database design: develops a model of what we want to represent, and how these should relate, ignoring the implementation issues. Data-driven approach, i.e., first think what data to represent and then what operations on the data to have (application programs). This phase is crucial to the successful usage of a database in an organization. A well-designed database system provides the correct information for the decision-making process to succeed, in an efficient way. In this course we will mostly learn how to correctly and efficiently realize this step. Physical database design: decides how we will realize the implementation using some concrete DBMS, e.g., MySQL, Oracle. We will use the very popular MySQL DBMS system to acquire experience in practical realization of a database system.

40 Advantages of DBMSs Control of data redundancy. Though, sometimes it is profitable to have some data redundancy in a database. For instance, additional indexes may improve efficiency of the databse search. Data consistency. Having data redundancy under control it is much easier to keep the data consistent (only single copy has to be updated instead of several copies of an object). Sharing of data. Improved data integrity. Achieved by the use of constraints (consistency rules) on the data in a single record and on the relationships between records. Improved maintenance through data independence: applications are independent from the data organization. Improved data security, accessibility, back-up/recovery services. Increased productivity and concurrency.

41 Disadvantages of DBMSs Complexity. DBMS is very complex piece of software, and all users must understand its functionality to take full adventage of it. Cost of DBMS. Can vary from only $100 for a single-user PC, to $100, 000 $1, 000, 000 for a large mainframe multi-user system. Cost of conversion. Cost of a DBMS may be insignificant compared with the cost of converting existing applications to run on the new DBMS and hardware (includes staff training, specialist staff to help with the conversion). Performance. DBMSs are general-purpose systems, and thus they may not be as efficient as some problem-specific software in some applications. Higher impact of a failure. Since all users and applications rely on the availability of the DBMS, the failure of any component can bring operations to a complete halt, until it is repaired.

42 Some common business areas covered by the discussed models are: Customer order entry Inventory control Asset management Project management Course management Human resources management Payroll management

43 Information about materials/sources for these slides The following main materials are used: T. Connolly and C. Begg, Database Solutions: A step-by-step guide to building databases, Addison-Wesley, Some transparencies are based on templates of Pearson Education Ltd, 2004.

LECTURE1: PRINCIPLES OF DATABASES

LECTURE1: PRINCIPLES OF DATABASES Ref. Chapter1 Information Systems Department Chapter1 - Objectives 2 Problems with file-based approach. Database concepts. Database Management System (DBMS). Major components