The document provides an overview of relational databases and their advantages over traditional file-based systems. It discusses key concepts such as entities, attributes, records, files and databases. The document also describes database management systems (DBMS), schemas, data dictionaries, and relational database structures including tables, rows, columns, primary keys and foreign keys. Relational databases organize data into logically related tables to facilitate data integration, sharing, flexibility and consistency.

1. HAPTER 4 Relational Databases

28. Database Enrollment by Class Logical View—User A Logical View—User B DBMS Operating System The DBMS translates users’ logical views into instructions as to which data should be retrieved from the database.

29. Database Enrollment by Class Logical View—User A Logical View—User B DBMS Operating System The operating system translates DBMS requests into instructions to physically retrieve data from various disks.

33. Subschema--User A Smith . . . A Jones . . . B Arnold . . .D Subschema--User B Subschema--User C Enroll Cash Receipt Classes Student Mapping external-level views to conceptual-level schema Mapping conceptual-level items to internal-level descriptions

35. Subschema--User A Smith . . . A Jones . . . B Arnold . . .D Subschema--User B Subschema--User C Enroll Cash Receipt Classes Student Mapping external-level views to conceptual-level schema Mapping conceptual-level items to internal-level descriptions

37. Subschema--User A Smith . . . A Jones . . . B Arnold . . .D Subschema--User B Subschema--User C Enroll Cash Receipt Classes Student Mapping external-level views to conceptual-level schema Mapping conceptual-level items to internal-level descriptions

38. Subschema--User A Smith . . . A Jones . . . B Arnold . . .D Subschema--User B Subschema--User C Enroll Cash Receipt Classes Student Mapping external-level views to conceptual-level schema Mapping conceptual-level items to internal-level descriptions The bidirectional arrows represent mappings between the schema.

56. Relation

58. Each row is called a tuple, which rhymes with “couple.”

59. Each row contains data about a specific occurrence of the type of entity in the table.

60. Each column in a table contains information about a specific attribute of the entity.

61. A primary key is the attribute or combination of attributes that uniquely identifies a specific row in a table.

62. In some tables, two or more attributes may be joined to form the primary key.

63. A foreign key is an attribute in one table that is a primary key in another table. 203 J.D. Radowski 1506 202 Xi Zhang 1503 316 Amy Melton 1419 420 Glen Howard 1418 Office No. First Name Last Name Advisor No. ADVISORS 1503 555-5555 Artie Moore 123-45-6789 1418 444-4444 Ned Sanders 111-11-1111 1418 333-3333 Alice Simpson 333-33-3333 Advisor No. Phone No. First Name Last Name Student ID STUDENTS

64. Foreign keys are used to link tables together. 203 J.D. Radowski 1506 202 Xi Zhang 1503 316 Amy Melton 1419 420 Glen Howard 1418 Office No. First Name Last Name Advisor No. ADVISORS 1503 555-5555 Artie Moore 123-45-6789 1418 444-4444 Ned Sanders 111-11-1111 1418 333-3333 Alice Simpson 333-33-3333 Advisor No. Phone No. First Name Last Name Student ID STUDENTS

65. Other non-key attributes in each table store important information about the entity. 203 J.D. Radowski 1506 202 Xi Zhang 1503 316 Amy Melton 1419 420 Glen Howard 1418 Office No. First Name Last Name Advisor No. ADVISORS 1503 555-5555 Artie Moore 123-45-6789 1418 444-4444 Ned Sanders 111-11-1111 1418 333-3333 Alice Simpson 333-33-3333 Advisor No. Phone No. First Name Last Name Student ID STUDENTS

78. Advisor No. is a foreign key in the STUDENTS table. Every incident of Advisor No. in the STUDENTS table either matches an instance of the primary key in the ADVISORS table or is null. 203 J.D. Radowski 1506 202 Xi Zhang 1503 316 Amy Melton 1419 420 Glen Howard 1418 Office No. First Name Last Name Advisor No. ADVISORS 1503 555-5555 Artie Moore 123-45-6789 1418 444-4444 Ned Sanders 111-11-1111 1418 333-3333 Alice Simpson 333-33-3333 Advisor No. Phone No. First Name Last Name Student ID STUDENTS