Page 104 - DCAP516_COMPUTER_SECURITY

Computer Security

Notes 8.12.2 Data Manipulation Language (DML)

Data Manipulation is:
1. Retrieval of information from the database
2. Insertion of new information into the database

3. Deletion of information in the database
4. Modification of information in the database
A DML is a language which enables users to access and manipulate data. The goal is to provide
efficient human interaction with the system.
There are two types of DML:
1. Procedural (the user specifies what data is needed and how to get it), and
2. Non-procedural (the user only specifies what data is needed; It is easier for user and may
not generate code as efficient as that produced by procedural languages)
A query language is a portion of a DML involving information retrieval only. The terms DML
and query language are often used synonymously.
8.13 Database Schema

It is the overall structure is called a database schema. Database schema is usually graphical
presentation of the whole database. Tables are connected with external keys and key columns.
When accessing data from several tables, database schema will be needed in order to find
joining data elements and in complex cases to find proper intermediate tables. Some database
products use the schema to join the tables automatically.
Database system has several schemas according to the level of abstraction. The physical schema
describes the database design at physical level. The logical schema describes the database design
at logical level. A database can also have subschema (view level) that describes different views
of database.

8.14 Database Instance

1. Databases change over time.
2. The information in a database at a particular point of time is called an instance of the
database.
3. Analogy with programming languages:
(i) Data type definition - scheme
(ii) Value of a variable - instance

8.15 Meta-Data

Meta-data is definitional data that provides information about or documentation of other data
managed within an application or environment. For example, meta-data would document data
about data elements or attributes, (name, size, data type, etc.) and data about records or data
structures (length, fields, columns, etc.) and data about data (where it is located, how it is

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