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UMBC CMSC 461 - Database Management Systems

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Chapter 1: IntroductionDatabase Management System (DBMS)Purpose of Database SystemsPurpose of Database Systems (Cont.)Levels of AbstractionView of DataInstances and SchemasData ModelsData Manipulation Language (DML)Data Definition Language (DDL)Relational ModelA Sample Relational DatabaseSQLDatabase DesignThe Entity-Relationship ModelStorage ManagementQuery ProcessingQuery Processing (Cont.)Transaction ManagementDatabase ArchitectureDatabase UsersDatabase AdministratorOverall System StructureHistory of Database SystemsHistory (cont.)End of Chapter 1Figure 1.4Figure 1.7Database System Concepts, 5th Ed.©Silberschatz, Korth and SudarshanSee www.db-book.com for conditions on re-use Chapter 1: IntroductionChapter 1: Introduction©Silberschatz, Korth and Sudarshan1.2Database System Concepts, 5th Ed., slide version 5.0, June 2005Database Management System (DBMS)Database Management System (DBMS)DBMS contains information about a particular enterpriseCollection of interrelated dataSet of programs to access the data An environment that is both convenient and efficient to use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©Silberschatz, Korth and Sudarshan1.3Database System Concepts, 5th Ed., slide version 5.0, June 2005Purpose of Database SystemsPurpose 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©Silberschatz, Korth and Sudarshan1.4Database System Concepts, 5th Ed., slide version 5.0, June 2005Purpose of Database Systems (Cont.)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©Silberschatz, Korth and Sudarshan1.5Database System Concepts, 5th Ed., slide version 5.0, June 2005Levels of AbstractionLevels 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.type customer = recordcustomer_id : number; 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.©Silberschatz, Korth and Sudarshan1.6Database System Concepts, 5th Ed., slide version 5.0, June 2005View of DataView of DataAn architecture for a database system©Silberschatz, Korth and Sudarshan1.7Database System Concepts, 5th Ed., slide version 5.0, June 2005Instances and SchemasInstances 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Instance – the actual content of the database at a particular point in time Analogous to the value of a variable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.©Silberschatz, Korth and Sudarshan1.8Database System Concepts, 5th Ed., slide version 5.0, June 2005Data ModelsData ModelsA collection of tools for describing Data Data relationshipsData constraintsRelational modelEntity-Relationship data model (mainly for database design) Object-based data models (Object-oriented and Object-relational)Semistructured data model (XML)Other older models:Network model Hierarchical model©Silberschatz, Korth and Sudarshan1.9Database System Concepts, 5th Ed., slide version 5.0, June 2005Data Manipulation Language (DML)Data Manipulation Language (DML)Language for accessing and manipulating the data organized by the appropriate data modelDML also known as query language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©Silberschatz, Korth and Sudarshan1.10Database System Concepts, 5th Ed., slide version 5.0, June 2005Data Definition Language (DDL)Data Definition Language (DDL)Specification notation for defining the database schemaExample: create table account ( account-number char(10), balance integer)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Consistency constraintsIntegrity constraintsDomain constraintsAssertionsAuthorization©Silberschatz, Korth and Sudarshan1.11Database System Concepts, 5th Ed., slide version 5.0, June 2005Relational


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