Database Management Systems, R. Ramakrishnan and J. Gehrke 1Introduction to Database SystemsDatabase Management Systems, R. Ramakrishnan and J. Gehrke 2Why Study Databases?? Shift from computation to information– at the “low end”: scramble to webspace (a mess!)– at the “high end”: scientific applications Datasets increasing in diversity and volume. – Digital libraries, interactive video, Human Genome project, EOS project – ... need for DBMS exploding DBMS encompasses most of CS– OS, languages, theory, “A”I, multimedia, logic?Database Management Systems, R. Ramakrishnan and J. Gehrke 3What Is a DBMS? A very large, integrated collection of data Models real-world enterprise– Entities (e.g., students, courses)– Relationships (e.g., Madonna is taking CS432) A Database Management System (DBMS) is a software package designed to store and manage databasesDatabase Management Systems, R. Ramakrishnan and J. Gehrke 4Why Use a DBMS? Reduced application development time (Queries) Data independence and efficient access Concurrent access Crash recovery Uniform data administrationDatabase Management Systems, R. Ramakrishnan and J. Gehrke 5Data Models A data model is a collection of concepts for describing data. A schemais a description of a particular collection of data, using the a given data model. The relational model of datais the most widely used model today.– Main concept: relation, basically a table with rows and columns.– Every relation has a schema, which describes the columns, or fields.Database Management Systems, R. Ramakrishnan and J. Gehrke 6QueriesDatabase Management Systems, R. Ramakrishnan and J. Gehrke 7Data Independence Applications insulated from how data is structured and stored. Physical data independence: Protection from changes in physical structure of data. Logical data independence: Protection from changes in logical structure of data. One of the most important benefits of using a DBMS!Database Management Systems, R. Ramakrishnan and J. Gehrke 8Concurrency ControlDatabase Management Systems, R. Ramakrishnan and J. Gehrke 9RecoveryDatabase Management Systems, R. Ramakrishnan and J. Gehrke 10Structure of a DBMS A typical DBMS has a layered architecture. The figure does not show the concurrency control and recovery components. This is one of several possible architectures; each system has its own variations.Query Optimizationand ExecutionRelational OperatorsFiles and Access MethodsBuffer ManagementDisk Space ManagementDBThese layersmust considerconcurrencycontrol andrecoveryDatabase Management Systems, R. Ramakrishnan and J. Gehrke 11Summary DBMS used to maintain, query large datasets.– Benefits include quick application development, data independence, concurrency control, recovery A DBMS typically has a layered architecture. DBMS R&D is one of the broadest, most exciting areas in CS. DBAs hold responsible jobs and are