Data Dictionary acts as an automated or a manual, active or a passive file which has the ability to store the definitions of the data elements and the data characteristics. The Data Dictionary is actually the repository of the information about the data. Data Dictionary defines each of the data elements and also gives it a name for the easy access.

Data Dictionary acts as the core or the hub of the database management system, is the third component of the database management system. The Data Dictionary provides with the following information –
1. The name of the data item.
2. The description of the data item.
3. The sources of the data.
4. The impact analysis.
5. Keywords that are used for the categorization and the search of the data item descriptions.

Functions of the Data Dictionary
1. Defines the data element.
2. Helps in the scheduling.
3. Helps in the control.
4. Permits the various users who know which data is available and how can it be obtained.
5. Helps in the identification of the organizational data irregularity.
6. Acts as a very essential data management tool.
7. Provides with a good standardization mechanism.
8. Acts as the corporate glossary of the ever growing information resource.
9. Provides the report facility, the control facility along with the excerpt facility.

The types of the database models generally used in the business organizations can be categorized as follows –

1. Hierarchical Data Base Model (HDBM)

a. Is one of the earliest data base management systems.
b. This model has data logically as one to many relationship.
c. Follows a structured organizational mode.
d. Requires a controlled, finite and a rule based approach.
e. Represents data in a pyramidal or a tree like structure.
f. Each record appears to be like an organizational chart with one top level segment, called the root, spreading downwards into the branches and the leaves.
g. There is a record.
h. Within each record, the data elements are organized into the pieces of record which are referred to as the segments.
i. An upper segment is linked to a lower segment in a parent child relationship.
j. A parent segment may have more than one child.
k. A child can have only one parent.
l. The most common hierarchical data base management system has been the Information Management System (IMS) released by the IBM in the year 1968.

2. Network Data Base Model (NDBM)

a. Acts as the variation of the above Hierarchical Data Base Model.
b. This model has data logically as many–to– many relationship.
c. Helps in understanding and also helps in analyzing the sales Zone performance.
d. Analysis the sales and the recovery position.
e. Analysis the product wise sales performance.

3. Relational Database Model (RDBM)

a. Most recent of the three database models.
b. Was proposed by Dr. E.F Cod in the year 1970.
c. Consists of the data in the database as simple two dimensional tables called as the relations.
d. The table consists of the rows and also the columns.
e. Rows represent the individual records.
f. The columns represent the attributes of each of the record.
g. The information in more than one file can be easily extracted.
h. This information can be further combined to suit the user’s specific requirements.
i. The three basic operations of this model are Select, Project, Join.

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Introduction
In the Management Information Systems, the concept of the ‘Systems’ play a very essential and a defining role and it can be surely referred to as the backbone of the management Information Systems. The major concept of the systems involves basically the pattern or a way in which one thinks about managing optimally. In management Information Systems, it acts as the framework for the visualization and the analysation of the internal as well as the external environments and the factors affect these particular environments in a very integrated way or pattern.

The word systems refer to as the arrangement or the way of organizing some specific things in a particular way. So now a system can be defined as the regularly interacting interdependent group of the items ultimately leading to the formation of a united whole. Particularly for the management Information Systems, a system consists of certain specific set of elements that can be identified as the belonging together because of the common purpose, goal or the objective.

The features defining the system usually act as its boundaries, so it can be said that the system is inside the boundary and the environment is outside the boundary.

Each system is further made of the sub systems, which further consist of the other subsystems and one very important point to be kept in mind here is that all of these subsystems are defined specifically by its boundaries. Each subsystem itself actually acts as the system. The Interconnections and the various interactions that generally take place between the various subsystems are referred to as the interfaces.

These interfaces are generally known to occur at the boundary and usually take the form of the inputs and the outputs. A system is not at all arranged randomly but is arranged with the help of certain logic, which are governed by the rules, the regulations, the principles, the policies etc. Such an arrangement of a system is generally influenced by the objective which the system always desires to achieve.

In the management Information Systems, the concept of the system is very much important and one should have an in depth knowledge of it as with the help of this, one can easily have a look at the individual elements, subsystems in the larger perspective of the whole system leading to the optimal solutions and the synergy.

There are different types of the system and are generally found to be present in all the fields of the endeavor. There are systems like the social system, political system, economic system etc.
All the Systems must possess the following –
1. Goals
2. Components
3. Subsystems
4. Behavior
5. Boundaries
6. Life cycle

What are the Characteristics of the System
A System must be having or possessing the following characteristics –
1. System receives inputs with the help of the information, energy or the materials.
2. System processes inputs and also produces outputs or the results.
3. System has a particular structure.
4. System is very much interdependent in the nature.
5. System has an objective orientation.