Lecture №9. Database systems.

Purpose: to provide an overview about Database Management Systems (DBMS) and introduce one of DBMS: SQL


1.Bases of database systems: concept, characteristic, architecture.

2. Data models. Normalization. Integrity constraint on data.


Bases of database systems: concept, characteristic, architecture.

Introduction to Databases.A database is a structured collection of records or data. A computer database is a kind of software to organize the storage of data. Databases help you organize this related information in a logical fashion for easy access and retrieval. To develop a database, there are several models used such as Hierarchical model, Network model, Relational model, Object-Oriented model etc.

Hierarchical model.In a hierarchical model, data is organized into an inverted tree-like structure. This structure arranges the various data elements in a hierarchy and helps to establish logical relationships among data elements of multiple files. Each unit in the model is a record which is also known as a node. Each record has a single parent.

Figure 1- Hierarchical Model

Network model. The network model tends to store records with links to other records. Each record in the database can have multiple parents, i.e., the relationships among data elements can have a many to many relationships. So this model is an expansion to the hierarchical structure, allowing many-to-many relationships in a tree-like structure that allows multiple parents.

The network model provides greater advantage than the hierarchical model in that it promotes greater flexibility and data accessibility.

Figure 2- Network Model

Relational model.The relational model for the database management is a database model based on relations. The basic data structure of the relational model is a table where information about a particular entity (say, a student) is represented in columns and rows. The columns enumerate the various attributes(i.e. characteristics) of anentity(e.g. student name, address, registration _number).The rows (also called records) represent instances of an entity (e.g. specific student).

Object –Oriented model.In this Model we have to discuss the functionality of the object oriented Programming. It takes more than storage of programming language objects. It provides full-featured database programming capability, while containing native language compatibility. It adds the database functionality to object programming languages. This approach is the analogical of the application and database development into a constant data model and language environment. Applications require less code, use more natural data modeling, and code bases are easier to maintain. Object developers can write complete database applications with a decent amount of additional effort. But object-oriented databases are more expensive to develop.

Data models. Normalization. Integrity constraint on data.

Database Management System. A Database Management System (DBMS) is computer software designed for the purpose of managing databases based on a variety of data models. A DBMS is a complex set of software programs that controls the organization, storage, management, and retrieval of data in a database. DBMS are categorized according to their data structures or types, sometime DBMS is also known as a Database Manager. Data management tasks fall into one of four general categories as given below:

Entering data into the database.

Housekeeping tasks such as updating data, deleting obsolete records, and backing up the database.

Sorting the data: arranging or re-arranging the database‟s records.

Obtaining subsets of data.

There are several advantages in DBMS such as reduced data redundancy and inconsistency, enhanced data integrity, improved security etc.

Normalization of databases is a process of transformation of database to the kind answering the normalized forms.

Classification of limitations of integrity

In the theory of relational databases it is accepted to distinguish four types of limitations of integrity:

· Limitation of database is name a limit on values that it is let to accept to the indicated database.

· Limiting to the variable of relation is name a limit on values that it is let to accept to the indicated variable of relation.

· Limitation of attribute is name a limit on values that it is let to accept to the indicated attribute.

· Limitation of type is not that another, as determination of great number of values this type consists of that.

Example of widespread restriction of level of a variable of the relation is the potential key; an example of widespread restriction of level of the database is the foreign key.

Integrity and truth of data in a DB

Integrity of a DB doesn't guarantee reliability (truth) of the information which is contained in it, but provides at least plausibility of this information, rejecting certainly improbable, impossible values. Thus, it isn't necessary to confuse integrity (consistency) of a DB to truth of a DB. Truth and consistency — not same.

Reliability (or truth) is compliance of the facts which are stored in the database, to the real world. It is obvious that determination of reliability of a DB requires possession of full knowledges both about DB contents, and about the real world. Determination of integrity of a DB requires only possession of knowledge of contents of a DB and about the rules set for it. Therefore the DBMS can't guarantee existence in the database only of the true expressions; all that she can make, are to guarantee absence of any data causing violation of integrity constraints (that is to guarantee that she doesn't contain any data not compatible to these restrictions).


1.What makes databases such an essential component of modern life?

2. Can databases be used to predict consumer behavior?

3. What are the basic components of a database?



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