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Edit Comment Close Premium member Presentation Transcript Databases: Databases Contents Terminology Relational databases Database design Other types of databases Summary A student’s lab report: A student’s lab report I applied a load of 100 Kg at the midspan of the beam. The dial gauge showed 4 mm deflection. Then I applied another 100 Kg load. Now the deflection increased to 8.5 mm. Terminology: Terminology Database: A collection of persistent and structured data Database management system: A software component that manages databases Database system: database + database management system Three-level architecture: Three-level architecture Application-level Conceptual-level Internal representation Types of databases: Types of databases hierarchical relational object-oriented logic-based distributed multi-media flat files Relational database systems: Relational database systems Based on the relational model by Codd E. F. Principal idea – organise data in the form of two-dimensional tables Standard set of operations for accessing and modifying data The relational model: The relational model Definition of an n-ary relation: (From set theory) An n-ary relation among sets: A1, A2, .. An is a subset of ( ( (A1 x A2) x .. ) x An) A set of ordered n-tuples RDBMS terminology n-ary relation - Table A1, A2, .. An - Domains: Columns n - degree of the table: Number of columns Each n-tuple is a row (record) Example of a relation: Example of a relation Table: Steel Plate Sections Definitions: Definitions Primary key: A domain of a table is called a primary key if its value in a record uniquely identifies the record in the table. Composite primary key: A cartesian product of two or more domains such that its value in a record uniquely identifies the record in the table Foreign key: A domain of a table is called a foreign key if its value refers to the primary key of another table. Candidate key is either a primary key or alternate key Definitions: Definitions Projection (View) A projection of a relation is an m-ary relation, m <= n obtained from R by deleting n-m of the components in each ordered n-tuple in R. (It is an abstraction of the original table). Join: Join Limitations of relational databases: Limitations of relational databases Records are of constant size! Variable size elements like lists are not supported! Exercise: Exercise Design a database to store details of leaf springs Accessing data: Accessing data GUI – graphical user interface API - application program interface SQL - Structure query language SQL- Structured Query Language: SQL- Structured Query Language Defines syntax for performing standard operations on databases Create tables Insert records Update records Delete records Join tables Project tables Examples: SQL: Examples: SQL CREATE TABLE emp_details ( first_name char(15) not null, last_name char(15) not null, comment text(50), dept char(20), emp_id int , PRIMARY KEY (emp_id) ) DROP TABLE table_name Examples: SQL: Examples: SQL SELECT first_name, last_name FROM emp_details WHERE dept = `civil' ORDER BY last_name, first_name DESC INSERT INTO steel_plates (Section-ID, Thickness, Width, Area) VALUES ('I-100', 12, 100, 1200) UPDATE emp_details SET salary=50000 WHERE emp_id = 1234 DELETE FROM emp_details WHERE emp_id = 12345 Relational database design: Relational database design A bad design results in maintenance problems Normal forms have been proposed to provide guidelines for good designs. Tables in a well-designed database exist in higher normal forms There are primarily five normal forms, denoted as 1NF, 2NF, 3NF, 4NF and 5NF + a special case of 3NF called the Boyce-Codd normal form First normal form: First normal form A relation is said to be in first normal form (1NF) if it contains only atomic (scalar) values Functional dependency : Functional dependency 2NF: 2NF Every non-key attribute is irreducibly dependent on the primary key. A relation in 2NF: A relation in 2NF A relation in 2NF: A relation in 2NF A relation not in 2NF: A relation not in 2NF Bridge details: Bridge details What are the functional dependencies? Is it in 2NF? Update anomalies: Update anomalies Redundancy Insert Update Delete 3NF: 3NF Every non-key attribute is mutually independent A relation in 3NF: A relation in 3NF A relation not in 3NF: A relation not in 3NF Update anomalies: Update anomalies Redundancy Insert Update Delete Transaction processing: Transaction processing A transaction is a logical unit of work (LUW). Either all requests in a transaction go through successfully, otherwise none of them go through Mechanisms for implementing transactions: Mechanisms for implementing transactions Locks Commit/Rollback Object databases: Object databases Need to store non-relational data Better integration with object-oriented systems Geographic databases: Geographic databases Relational model inefficient for storing geographic information Multimedia databases: Multimedia databases Mixture of structured and unstructured data Usually multi-media data is stored in files, meta-data in relational databases Applications in air-traffic control, entertainment Distributed databases: Distributed databases Storing all data on a single computer creates scalability problems. Distributing data on multiple machines creates issues related to ensuring integrity and consistency across machines. Summary: Summary Data should be properly organised – for ease of retrieval and maintainability DBMSs allow sharing data across applications Relational databases are simple and efficient Good database design requires knowledge of FDs You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.