Билет № 7

Прочтите и переведите письменно со словарем ИИТУ

Databases and Database Management Systems

A database is a collection of related data or facts arranged in a specific structure. A database management system (DBMS) is a program, or collection of programs, that allows multiple users to store, access, and process data or facts into useful information. Three of the most important terms to know about databases are a table, a record, a field. Data is stored in tables. A table is divided into records, and each record is divided into fields. The table consists of a set number of fields and an arbitrary number of records. For a record to exist, it must have data in at least one field. To help you understand how a database stores data, think about a typical address book. Each piece of information in the address book is stored in its own location, called a field. For example, each entry has a field for First Name and another field for Last Name, as well as fields for Address, City, State, ZIP Code, and Phone Number. Each unique type of information is stored in its own field. One full set of fields – that is, all the related information about one person or object – is called a record. Therefore, all the information for the first person is record 1, all the information for the second person is record 2, and so on. A complete collection of records makes a table. Once you have a structure for storing data, you can enter and view data, create reports, and perform other tasks with the data. For example, you may create a customer report that lists customers by ZIP Code. A DBMS provides tools to perform data management functions: creating tables, sorting tables, entering and editing data, querying the database, viewing data, generating reports.

Билет № 8

Прочтите и переведите письменно со словарем ИИТУ

Database Structures

There are several types of database structures, such as flat-file, relational, hierarchical, network and object-oriented ones. A database that consists of a single data table is called a flat-file database. Flat-file databases are useful for certain single-user or small-group situations, especially for maintaining address lists or inventories. Flat-file database systems are easy to learn and use, but difficult to maintain and limited in their power. When numerous files exist, there is often a lot of data redundancy, which increases the chance for errors, wastes time, and uses excess storage space. A relational database is made up of a set of tables, and a common field existing in any two tables creates a relationship between the tables. For example, a Customer ID Number field in both the Customers table and the Orders table links the two tables, while a Product ID field links the Orders and Products tables. The relational database structure is widely used in today's business organizations. In a business, a typical relational database contains such data tables, as Customer information, Employee information, Vendor information, Order information, Inventory information. The hierarchical database is an older style of database. The tables are organized into a fixed treelike structure, with each table storing one type of data. The trunk table stores general information. Any field in that table may reference another table that contains subdivisions of data. Each one of those tables may, in turn, reference other tables that store finer subdivisions of data. The relationship between tables is said to be a parent-child relationship, or one-to many relationship, with any child table relating to only one parent table. Each parent table may have many child tables, but each child has only one parent. Hierarchical databases require little duplicated data and may locate data quickly.