Chapter 15

• Data is retrieved quickly from a database.
• Data is updated in a database.
• Data is filtered in a database.
• Different users can see only specific amounts of data in a database.
• A view is a subset of data tailored for a particular user or a particular application.
• Organisations that maintain a good-quality database can be sure that all their users have access to the one up-to-date copy of the data and there is less danger of inconsistencies, leading to errors.
• In the early days of commercial computer applications, data was stored in separate files.
• These files reflected the nature of the storage techniques at the time and were typically serial or sequential files.
• Most data was stored on magnetic tape, which was written to or read from in an orderly sequence.
• Flat file databases store all the data in a single table.
• This is sufficient if there is only a small amount of data.
• Flat file databases are useful when data is mostly static, i.e., it doesn’t change frequently.
• Most databases deal with lots of data that is dynamic, and so they need to provide a centralised and automated way of manipulating data.
• Quick to set up, require little expertise to maintain, suitable to store small amounts of data, can be inefficient, repetitive data, take up unnecessary space, slow to query, become difficult to maintain.
• Relational databases are the most common model of data organisation, devised by Edgar Codd in the late 1960s.
• Data is held in more than one table, and the tables are linked together using relationships.
• Relationships in relational databases are implemented using primary and foreign keys.
• Rules for relational database tables: every row must be constructed in the same way; that is, each column must contain data of just one data type, one column, or combination of columns, must be able to make each row of the table unique, which is called the primary key, there is no rule about the sequence of rows in a table, there is no rule about the order of the columns, no two tuples (rows) in a relation can be identical.
• A database is an organised collection of data that allows for easy modification, addition, deletion, search, sort, and extraction of information.
• Data needs to be related, meaning there needs to be a logical connection between the data so they can be combined for the same purpose.
• Data has been organized using paper-based filing systems and databases long before the mass use of computing technology.
• Organizing data in databases allows us to extract information from data and use it to solve a problem.
• Data can be stored in a computer.
• Electronic databases benefit from being easier to retrieve, add, delete, update, and modify data, and are easily accessed by multiple people from different locations.
• Data refers to values, measurements, facts, or observations that are collected and structured in a format that can be further processed.
• Information requires a certain knowledge about the data itself and the domain they belong to, to transform data into information.
• A table is a collection of related data arranged in the database in a table format made up of columns and rows.
• Fields in a database table are used to provide category headings for each item of data in the database.
• A record in a database table is a collection of data for a set of fields.
• Each row in a database table corresponds to a single record.
• A primary key in a database table is a field or set of fields that uniquely identifies each record in the table.
• A foreign key in a database table is a field or a set of fields that appears as the primary key in another table.
• Database applications are software programs designed to retrieve, manage, distribute, and present information effectively.
• Database applications can provide security by regulating access to data using user accounts and access rights.
• Entity is used to represent an object in the real world that can be distinguished from other objects and can be a physical object or a concept that is needed to record data in the database.
• Attribute represents a property, quality, or a characteristic that describes an entity.
• An entity has a value for each of its attributes, these make up the main body of data that is stored in the database.
• Sometimes an attribute can accept a null value.
• Each set of values that corresponds to a specific entity is called an instance of the entity.
• An entity identifies, also called a key attribute, is needed to distinguish between the different instances of an entity.