Before You Begin Limitations and Restrictions The database cannot be made smaller than the minimum size of the database. For example, if a database was originally created with a size of 10 MB and grew to MB, the smallest size the database could be reduced to is 10 MB, even if all the data in the database has been deleted. You cannot shrink a database while the database is being backed up. Conversely, you cannot backup a database while a shrink operation on the database is in process.
The types of files used are discussed first, followed by a description of the many ways conventional files can be organized. Master files and table files are used to store data for a long period.
The temporary files are usually called transaction files, work files, or report files.
Master Files Master files contain records for a group of entities. The attributes may be updated often, but the records themselves are relatively permanent. These files tend to have large records containing all the information about a data entity.
Each record usually contains a primary key and several secondary keys. Although the analyst is free to arrange the data elements in a master file in any order, a standard arrangement is to place the primary key field first, followed by descriptive elements, and finally by elements that change frequently with business activities.
Examples of a master file include patient records, customer records, a personnel file, and a parts inventory file. Table Files A table file contains data used to calculate more data or performance measures.
One example is a table of postage rates used to determine the shipping costs of a package. Another example is a tax table. Table files usually are read only by a program. Transaction Files A transaction file is used to enter changes that update the master file and produce reports.
Suppose a newspaper subscriber master file needs to be updated; the transaction file would contain the subscriber number, and a transaction code such as E for extending the subscription, C for canceling the subscription, or A for address change. Then only information relevant to the updating needs to be entered; that is, the length of renewal if E, and the address if A.
No additional information would be needed if the subscription were canceled. The rest of the information already exists in the master file. Transaction files may contain several different types of records, such as the three used for updating the newspaper subscription master, with a code on the transaction file indicating the type of transaction.
Report Files When it is necessary to print a report when no printer is available e.
A text file is sometimes called a flat file especially when comparing to a relational database. This is because a relational database is built to highlight how some data relates to other data. Flat file and relational databases. A database is a collection of data, which is organized into files called tables. These tables provide a systematic way of accessing, managing, and updating data. Files. A file contains groups of records used to provide information for operations, planning, management, and decision making. The types of files used are discussed first, followed by a description of the many ways conventional files can be organized.
Sending the output to a file rather than a printer is called spooling. Later, when the device is ready, the document can be printed.
Report files are very useful, because users can take files to other computer systems and output to specialty devices. Relational Databases Databases can be organized in several ways.
The most common type of database is a relational database. A relational database is organized in meaningful tables, which minimizes the repetition of data, which in turn minimizes errors and storage space.
It is clear that the users all see the data in different ways. We refer to the way a user pictures and describes the data as a user view. The problem, however, is that different users have different user views. These views need to be examined by the systems analyst, and an overall logical model of the database developed.
Finally, the logical model of the database must be transformed into a corresponding physical database design. Physical design is involved with how data are stored and related, as well as how they are accessed.
In database literature, the views are referred to as schema. Database design includes synthesizing user reports, user views, and logical and physical designs. There are three main types of logically structured databases: The first two types may be found in legacy older systems.
An analyst today would typically design a relational database. The rows of the table represent the records, and the columns contain attributes.
In a relational data structure, data are stored in many tables. Maintaining the tables in a relational structure is usually quite simple when compared with maintaining a hierarchical or network structure.
One of the primary advantages of relational structures is that ad hoc queries are handled efficiently. When relational structures are discussed in database literature, different terminology is often used.
A file is called either a table or relation, a record is usually referred to as a tuple, and the attribute value set is called a domain. For relational structures to be useful and manageable, the relational tables must first be normalized.Relational databases are also called Relational Database Management Systems (RDBMS) or SQL databases.
Historically, the most popular of these have been Microsoft SQL Server, Oracle Database, MySQL, and IBM DB2. A database is an application that can store and retrieve data very rapidly. The relational bit refers to how the data is stored in the database and how it is organized.
When we talk about a database, we mean a relational database, in fact, an RDBMS: Relational Database Management System.
In a. Flat file and relational databases. A database is a collection of data, which is organized into files called tables. These tables provide a systematic way of accessing, managing, and updating data. A database is an organization of data where the data content is organized in a structured way.
The structure is intended to provide the ability to define relations (the ‘Relational’ part of Relational Databases) between the elements of the data structure.
Relational databases store and manage data in a traditional table format, with each piece of data organized into a row and a column. Columns hold the data of a single type or field, like first name, order number, or the image link of a product logo.
When it comes to relational databases, I can’t help thinking that something is missing. They’re used everywhere. There are many different databases: from the small and useful SQLite to the powerful Teradata.