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DATABASE MANAGEMENT SYSTEMS

DATABASE MANAGEMENT SYSTEMS. Contents. Introduction to DBMS DBMS Users DBMS architecture Data Models ER Modeling Relational Model SQL Normalization. What Is a DBMS?. Database : A very large, integrated collection of data.

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DATABASE MANAGEMENT SYSTEMS

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  1. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS DATABASE MANAGEMENT SYSTEMS

  2. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Contents • Introduction to DBMS • DBMS Users • DBMS architecture • Data Models • ER Modeling • Relational Model • SQL • Normalization

  3. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS What Is a DBMS? • Database : A very large, integrated collection of data. • A DatabaseManagementSystem(DBMS)is a software package designed to store and manage databases.

  4. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Database System Applications • Database Applications: • Banking: all 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 touch all aspects of our lives

  5. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS

  6. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS

  7. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS

  8. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS

  9. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS

  10. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Purpose of Database Systems • In the early days, database applications were built directly on top of file systems • 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

  11. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Purpose of Database Systems (Cont.) • Drawbacks of using file systems (cont.) • Atomicity of updates • Failures may leave database in an inconsistent state with partial updates carried out • Example: Transfer of funds from one account to another should either complete or not happen at all • Concurrent access by multiple users • Concurrent accessed needed for performance • Uncontrolled concurrent accesses can lead to inconsistencies • Example: Two people reading a balance and updating it at the same time • Security problems • Hard to provide user access to some, but not all, data • Database systems offer solutions to all the above problems

  12. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Why Use a DBMS? • Data independence and efficient access. • Reduced application development time. • Data integrity and security. • Uniform data administration. • Concurrent access, recovery from crashes.

  13. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Database Users Users are differentiated by the way they expect to interact with the system • Application programmers – interact with system through DML calls • Sophisticated users – form requests in a database query language • Naïve users – invoke one of the permanent application programs that have been written previously • Examples, people accessing database over the web, bank tellers, clerical staff

  14. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Database Administrator • Coordinates all the activities of the database system • has a good understanding of the enterprise’s information resources and needs. • Database administrator's duties include: • Storage structure and access method definition • Schema and physical organization modification • Granting users authority to access the database • Backing up data • Monitoring performance and responding to changes

  15. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS View of Data An architecture for a database system

  16. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Levels of Abstraction • Physical level: describes how a record (e.g., customer) is stored. • Logical level: describes data stored in database, and the relationships among the data. typecustomer = record customer_id : string; customer_name : string;customer_street : string;customer_city : string; end; • View level: application programs hide details of data types. Views can also hide information (such as an employee’s salary) for security purposes.

  17. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Instances and Schemas • Similar to types and variables in programming languages • Schema – the logical structure of the database • Example: The database consists of information about a set of customers and accounts and the relationship between them) • Analogous to type information of a variable in a program • Physical schema: database design at the physical level • Logical schema: database design at the logical level

  18. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Instances and Schemas • Physical Data Independence – the ability to modify the physical schema without changing the logical schema • Applications depend on the logical schema • In general, the interfaces between the various levels and components should be well defined so that changes in some parts do not seriously influence others.

  19. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Data Independence • Applications insulated from how data is structured and stored. • Logical data independence:Protection from changes in logical structure of data. • Physicaldata independence:Protection from changes in physical structure of data. • One of the most important benefits of using a DBMS!

  20. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS History of Database Systems • 1950s and early 1960s: • Data processing using magnetic tapes for storage • Tapes provide only sequential access • Punched cards for input • Late 1960s and 1970s: • Hard disks allow direct access to data • Network and hierarchical data models in widespread use • Ted Codd defines the relational data model • Would win the ACM Turing Award for this work • IBM Research begins System R prototype • UC Berkeley begins Ingres prototype • High-performance (for the era) transaction processing

  21. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS History (cont.) • 1980s: • Research relational prototypes evolve into commercial systems • SQL becomes industry standard • Parallel and distributed database systems • Object-oriented database systems • 1990s: • Large decision support and data-mining applications • Large multi-terabyte data warehouses • Emergence of Web commerce • 2000s: • XML and XQuery standards • Automated database administration • Increasing use of highly parallel database systems • Web-scale distributed data storage systems

  22. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Data Models • A datamodelis a collection of concepts for describing data. • Relational model • Entity-Relationship data model (mainly for database design) • Object-based data models (Object-oriented and Object-relational) • Semi structured data model (XML) • Other older models: • Network model • Hierarchical model • The relational model of datais the most widely used model today.

  23. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Database Design- Conceptual design:(ER Model) • A database can be modeled as: • a collection of entities, • relationship among entities. • An entityis an object that exists and is distinguishable from other objects. • Example: specific person, company, event, plant • Entities have attributes • Example: people have names and addresses • An entity set is a set of entities of the same type that share the same properties. • Example: set of all persons, companies, trees, holidays • Relationship:Association among two or more entities. E.g., Aisha works in Pharmacy department

  24. name ssn lot Employees Policies policyid cost www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS ER-diagram pname age Dependents Covers

  25. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Relational Model Attributes • Example of tabular data in the relational model

  26. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS A Sample Relational Database

  27. name ssn lot Employees www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Logical DB Design: ER to Relational • Entity sets to tables: SSN Name lot

  28. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS INTRODUCTION TO SCHEMA REFINEMENT Problems Caused by Redundancy • Storing the same information redundantly, that is, in more than one place within a database, can lead to several problems: • Redundant storage: Some information is stored repeatedly. • Update anomalies: If one copy of such repeated data is updated, an inconsistency is created unless all copies are similarly updated. • Insertion anomalies: It may not be possible to store some information unless some other information is stored as well. • Deletion anomalies: It may not be possible to delete some information

  29. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Bad DB Design to good DB Design • Informal method • Informal design guidelines • Formal method - Normalization

  30. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Normal Forms • If a relation is in a certain normal form (BCNF, 3NFetc.), it is known that certain kinds of problems are avoided/minimized. This can be used to help us decide whether decomposing the relation will help. • FDs are used to detect redundancy

  31. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Example decomposition(simple) • Bad database design • Good database design Eno Ename Salary Add Bdate Dno Dname Mngname Eno Ename Salary Add Bdate Dno Dno Dname Mngname

  32. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Data Definition Language (DDL) • Specification notation for defining the database schema Example: create tableaccount (account_numberchar(10), branch_name char(10), balanceinteger) • DDL compiler generates a set of tables stored in a data dictionary • Data dictionary contains metadata (i.e., data about data) • Database schema • Data storage and definition language • Specifies the storage structure and access methods used • Integrity constraints • Domain constraints • Referential integrity (e.g. branch_name must correspond to a valid branch in the branch table) • Authorization

  33. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Data Manipulation Language (DML) • Two classes of languages • Procedural – user specifies what data is required and how to get those data • Declarative (nonprocedural) – user specifies what data is required without specifying how to get those data • SQL is the most widely used query language

  34. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS SQL • SQL: widely used non-procedural language • Example: Find the name of the customer with customer-id 192select customer_namefrom customerwherecustomer_id = 192 • Example: Find the balances of all accounts held by the customer with customer-id 192 selectbalancefrom depositor, accountwherecustomer_id = 192 and depositor.account_number = account.account_number

  35. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS SQL • Application programs generally access databases through one of • Language extensions to allow embedded SQL • Application program interface (e.g., ODBC/JDBC) which allow SQL queries to be sent to a database

  36. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Query Processing 1.Parsing and translation 2. Optimization 3. Evaluation

  37. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Query Processing (Cont.) • Alternative ways of evaluating a given query • Equivalent expressions • Different algorithms for each operation • Cost difference between a good and a bad way of evaluating a query can be enormous • Need to estimate the cost of operations • Depends critically on statistical information about relations which the database must maintain • Need to estimate statistics for intermediate results to compute cost of complex expressions

  38. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Transaction Management • A transaction is a collection of operations that performs a single logical function in a database application • Transaction-management component ensures that the database remains in a consistent (correct) state despite system failures (e.g., power failures and operating system crashes) and transaction failures. • Concurrency-control manager controls the interaction among the concurrent transactions, to ensure the consistency of the database.

  39. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Transaction Concept • A transactionis a unit of program execution that accesses and possibly updates various data items. • E.g. transaction to transfer $50 from account A to account B: 1. read(A) 2. A := A – 50 3. write(A) 4. read(B) 5. B := B + 50 6. write(B) • Two main issues to deal with: • Failures of various kinds, such as hardware failures and system crashes • Concurrent execution of multiple transactions

  40. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Example of Fund Transfer • Transaction to transfer $50 from account A to account B: 1. read(A) 2. A := A – 50 3. write(A) 4. read(B) 5. B := B + 50 6. write(B) • Atomicity requirement • if the transaction fails after step 3 and before step 6, money will be “lost” leading to an inconsistent database state • Failure could be due to software or hardware • the system should ensure that updates of a partially executed transaction are not reflected in the database • Durability requirement — once the user has been notified that the transaction has completed (i.e., the transfer of the $50 has taken place), the updates to the database by the transaction must persist even if there are software or hardware failures.

  41. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Example of Fund Transfer (contd..) • Transaction to transfer $50 from account A to account B: 1. read(A) 2. A := A – 50 3. write(A) 4. read(B) 5. B := B + 50 6. write(B) • Consistency requirement in above example: • the sum of A and B is unchanged by the execution of the transaction • A transaction must see a consistent database. • During transaction execution the database may be temporarily inconsistent. • When the transaction completes successfully the database must be consistent • Erroneous transaction logic can lead to inconsistency

  42. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Example of Fund Transfer (Cont.) • Isolation requirement — if between steps 3 and 6, another transaction T2 is allowed to access the partially updated database, it will see an inconsistent database (the sum A + B will be less than it should be).T1 T2 1. read(A) 2. A := A – 50 3. write(A) read(A), read(B), print(A+B) 4. read(B) 5. B := B + 50 6. write(B • Isolation can be ensured trivially by running transactions serially • that is, one after the other. • However, executing multiple transactions concurrently has significant benefits.

  43. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS ACID Properties A transaction is a unit of program execution that accesses and possibly updates various data items.To preserve the integrity of data the database system must ensure: • Atomicity. Either all operations of the transaction are properly reflected in the database or none are. • Consistency. Execution of a transaction in isolation preserves the consistency of the database. • Isolation. Although multiple transactions may execute concurrently, each transaction must be unaware of other concurrently executing transactions. Intermediate transaction results must be hidden from other concurrently executed transactions. • That is, for every pair of transactions Tiand Tj, it appears to Tithat either Tj, finished execution before Ti started, or Tj started execution after Ti finished. • Durability. After a transaction completes successfully, the changes it has made to the database persist, even if there are system failures.

  44. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Transaction State

  45. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Concurrent Executions • Multiple transactions are allowed to run concurrently in the system. Advantages are: • increased processor and disk utilization, leading to better transaction throughput • E.g. one transaction can be using the CPU while another is reading from or writing to the disk • reduced average response time for transactions: short transactions need not wait behind long ones. • Concurrency control schemes– mechanisms to achieve ACID properties with concurrency. • Concurrency control protocols are used in DBMSs to control concurrency

  46. www.BookSpar.com | Website for Students | VTU NOTES -QUESTION PAPERS Overall System Structure

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