database concepts pdf :BEMIT

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NATIONAL INSTITUTE OF TRANSPORT
(NIT)
DEPARTMENT OF MATHEMATICS, HUMANITIES AND SOCIAL
SCIENCES.
COURSE: HIGHER DIPLOMA OF EDUCATION WITH MATHEMATICS AND IT.
MODULE: DATABASE CONCEPTS.
MODULE CODE: ITU 07306M
LECTURER: DUNSTAN PHARLES
NAME: MCHINJA, Usman A.
REG NO: NIT/BEMIT/2016/135.
TASK: Individual assignment 1.
SUBMISSION DATE: 13th December 2017.

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1. To write short notes on:
a) Derived attribute
 This is a function that maps from the entity set into a domain, whereby its
value can be derived from the values of other related attributes or entities.
For example the Lecturer entity set has an attribute age that indicates the
Lecturer’s age. If the Lecturer entity set also has an attribute date of birth,
we can calculate age from date of birth and the current date (Silberschatz
Et Al. 2011).
b) Data Flow Diagram
 Data flow diagrams (DFDs) is the diagram which reveals the relationships
among and between the various components in a program or system. DFDs
are an important technique for modeling a system’s high-level detail by
showing how input data can be transformed to output results through a
sequence of functional transformations. DFDs consist of four major
components which are entities, processes, data stores, and data flows.
(Donald 2017)
Figure 1: data flow diagram; Retrieved from https://www.visual-paradigm.com/tutorials/data-
flow-diagram-example-supermarket-app.jsp

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c) Database and DBMS
 The database is a collection of data, which stores the data required for a
given task in an organised way, grants access to them, and at the same
time safeguards the integrity of the units, and protects them from any harm
(Elmasri, Ramez. 2011).
And
 A database-management system (DBMS) is a collection of interrelated
data and a set of programs to access those data.
d) ER Model
 The ER model is the abbreviation of Entity Relational Model. It defines the
conceptual view of a database The ER model is very useful in mapping the
meanings and interactions of real-world enterprises onto a conceptual
schema. Because of this usefulness, many database-design tools draw on
concepts from the E-R model. The E-R data model uses the three basic
concepts which are entity sets, relationship sets, and attributes.
e) SQL as a high level language used DB Access
 The name SQL is presently expanded as Structured Query Language. It was
originally called SEQUEL (Structured English Query Language) and was
designed and implemented at IBM Research as the interface for an
experimental relational database system called SYSTEM R. An SQL
language is now the standard language for commercial relational DBMS’s.
2. To define Relational Database and distinguish it from a Table.
 Relational Database is a database which is based on the relational model
that means it presents information in tables with rows and columns. It uses
a collection of tables to represent both data and the relationships among
those data. It also includes a DML and DDL
 A table is referred to as a relation in the sense that it is a collection of objects
of the same type (rows).
Thus the major difference between the relational database and table is:

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 Data in a table can be related according to common keys or concepts, and
the ability to retrieve related data from a table is the basis for the term
relational database.
3. . A 3-Tier Architecture separates its Tiers from each other based on the complexity of the
users and how they use the data present in the DB, hence the most widely used Architecture
to design a DBMS
By use of the 3-Tier Architecture, illustrate how the functional process Logic, Data Access,
Computer Data Storage and User Interface are developed and maintained as Independent
modules on separate platforms.
Solution:
The 3-Tier Architecture facilitates what is called data independence. Data independence
can be defined as the capacity to change the schema at one level of a database system
without having to change the schema at the next higher level. We can define two types of
data independence as Logical data independence and physical data independence.
By using 3-tier architecture the functional process logic must be separated from Data
Access, Computer Data Storage and User Interface as follows using the two types of
independencies;
 Logical data independence;
This is the capacity to change the conceptual schema without having to change external schemas
or application programs. We may change the conceptual schema to expand the database (by adding
a record type or data item), to change constraints, or to reduce the database (by removing a record
type or data item) in a way that external schemas that refer only to the remaining data should not
be affected. Here the logical data is separated from physical data (that is data access, user interface
and computer Data storage is separated) (Shweta, 2009).
The following is the diagram showing the independencies;

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Figure 2: logical data independence; retrieved from http://player.slideplayer.com/16/5212349/#
 Physical data independence:
This is the capacity to change the internal schema without having to change the conceptual schema.
Hence, the external schemas should not be changed as well. Changes to the internal schema is
needed because some physical files were reorganized, for example, by creating additional access
structures to improve the performance of retrieval or update. If the same data as before remains in
the database, we should not have to change the conceptual schema. This means that physical data
(data access, user interface and computer Data storage) is separated from the logical data
(conceptual schema) (Shweta, 2009).
Figure 3 : Physical data independence; retrieved from https://www.tutorialcup.com/dbms/data-
independence.htm

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4. a) To mention and explain at least four Database utilities.
i. Loading utilities:
A loading utility is used to load existing data files-such as text files or sequential files-into the
database. Usually, the current (source) format of the data file and the desired (target) database file
structure are specified to the utility, which then automatically reformats the data and stores it in
the database. With the proliferation of DBMSs, transferring data from one DBMS to another is
becoming common in many organizations. Some vendors are offering products that generate the
appropriate loading programs, given the existing source and target database storage descriptions
(internal schemas). Such tools are also called conversion tools (Shweta, 2009).
ii. Backup utilities:
A backup utility creates a backup copy of the database, usually by dumping the entire database
onto tape. The backup copy can be used to restore the database in case of catastrophic failure.
Incremental backups are also often used, where only changes since the previous backup are
recorded. Incremental backup is more complex but saves space (Shweta, 2009).
iii. File Reorganization utilities:
This utility can be used to reorganize a database file into a different file organization to improve
performance.
iv. Performance Monitoring utilities:
Such a utility monitors database usage and provides statistics to the DBA. The DBA uses the
statistics in making decisions such as whether or not to reorganize files to improve performance
(Shweta, 2009).
b) Define and write short notes on:
i. DDL
Data-definition language (DDL).
The DDL provides commands for defining relation schemas, deleting relations, and modifying
relation schemas used by the DBA and by database designers to define both schemas. The
DBMS will have a DDL compiler whose function is to process DDL statements in order to
identify descriptions of the schema constructs and to store the schema description in the catalog.

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Examples of commands statements for DDL are CREATE, ALTER, DROP, TRUNCATE,
COMMENT, and RENAME (Tibor, 2011).
ii. DML
Once the database schemas are compiled and the database is populated with data, users must have
some means to manipulate the database. Typical manipulations include retrieval, insertion,
deletion, and modification of the data. The DBMS provides a set of operations or a language called
the data manipulation language (DML) for these purposes. The examples of DML statements
are SELECT, INSERT, UPDATE, DELETE, MERGE, CALL, EXPLAIN PLAN and LOCK
TABLE.
iii. Attribute:
An attribute of an entity set is a function that maps from the entity set into a domain. Since an
entity set may have several attributes, each entity can be described by a set of (attribute, data value)
pairs, one pair for each attribute of the entity set. They are descriptive properties possessed by each
member of an entity set. It expresses that the database stores similar information concerning each
entity in the entity set; however, each entity may have its own value for each attribute.
iv. Relationship in DBMS
A relationship is an association among several entities. Relationships are mapped with entities in
various ways. Mapping cardinalities define the number of association between two entities.
Mapping cardinalities: one to one, one to many, many to one, many to many

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5. a) To explain the advantages of DBMS
i. Data independence and efficient access.
Since database application programs are independent of the details of data representation and
storage, this means that the conceptual and external schemas provide independence from physical
storage decisions and logical design decisions respectively. Also a DBMS provides efficient
storage and retrieval mechanisms, including support for very large files, index structures and query
optimization.
ii. Reduced application development time.
Since the DBMS provides several important functions required by applications, such as
concurrency control and crash recovery, high level query facilities, etc., only application-specific
code needs to be written. Even this is facilitated by suites of application development tools
available from vendors for many database management systems.
iii. Data integrity and security.
The view mechanism and the authorization facilities of a DBMS provide a powerful access control
mechanism. Further, updates to the data that violate the semantics of the data can be detected and
rejected by the DBMS if users specify the appropriate integrity constraints.
iv. Data administration.
By providing a common umbrella for a large collection of data that is shared by several users, a
DBMS facilitates maintenance and data administration tasks. A good DBA can effectively shield
end-users from the chores of fine-tuning the data representation and periodic back-ups.
v. Concurrent access
A DBMS supports the notion of a transaction, which is conceptually a single user’s sequential
program. Users can write transactions as if their programs were running in isolation against the
database. The DBMS executes the actions of transactions in an interleaved fashion to obtain good

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performance, but schedules them in such a way as to ensure that conflicting operations are not
permitted to proceed concurrently.
vi. Crash recovery.
The DBMS maintains a continuous log of the changes to the data, and if there is a system crash, it
can restore the database to a transaction-consistent state. That is, the actions of incomplete
transactions are undone, so that the database state reflects only the actions of completed
transactions. Thus, if each complete transaction, executing alone, maintains the consistency
criteria, then the database state after recovery from a crash is consistent.
b) To Compare and contrast the Traditional System and the DBMS
 Difference between File processing system and DBMS:
i. A database management system (DBMS) coordinates both the physical and the logical
access to the data, whereas a file-processing system coordinates only the physical
access.
ii. A database management system is designed to allow flexible access to data (i.e. queries),
whereas a file-processing system is designed to allow predetermined access to data (i.e.
compiled programs).
iii. A database management system is designed to coordinate multiple users accessing the
same data at the same time while a file-processing system is usually designed to allow
one or more programs to access different data files at the same time. In a file-processing
system, a file can be accessed by two programs concurrently only if both programs have
read-only access to the file.
iv. Redundancy is control in DBMS, but not in file system.
v. Unauthorized access is restricted in DBMS but not in the file system.
vi. DBMS provide backup and recovery whereas data lost in file system can't be recovered.
vii. DBMS provide multiple user interfaces while Data is isolated in file system.

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 Similarities between DBMS and file-processing system:
i. Both DBMS and file-processing system are storing data on a permanent storage media. For
example, both have the concept of block level storage that is database blocks and filesystem
blocks - which is the smallest contiguous number of bytes for physically storing the
information.
ii. Both database and file-processing system have "indexes" which speed up access to the
data. There is also a consideration of migration where by both database and filesystem
migration entailed one key requirements: whenever data is being move, reading and
writing to the data must be halted/disabled. The migration can be online migration or
offline migration (Elmasri, Ramez. 2011).
iii. Both filesystem and database concept have the four key element properties of transactions
that is ACID. ACID stands for Atomicity (Atomicity represents the fact that a transaction
is an indivisible unit of execution), Consistency (Consistency demands that the carrying
out of the transaction does not violate any of the integrity constraints defined on the
database), Isolation (Isolation demands that the execution of a transaction is independent
of the simultaneous execution of other transactions ) and Durability (demands that the
effect of a transaction that has correctly executed a commit is not lost. In practice, a
database must guarantee that no piece of data is lost for any reason (Elmasri, Ramez, 2011).

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REFERENCES
Donald S (2017). Understanding Data Flow Diagrams Retrieved from
https://ratandon.mysite.syr.edu/cis453/notes/DFD_over_Flowcharts.pdf on 12 December 2017
at 15:16 PM.
Elmasri, Ramez. (2011).Fundamentals of database systems.6th edition. New York. Pearson
Education
Shweta (2009). Database Management System (DBMS).retrieved from http://database-
management-systems.blogspot.com/2009/09/database-system-utilities.html
Silberschatz Et Al. (2011). Database system concepts, sixth edition. New York, NY 10020. The
McGraw-Hill Companies
Tibor (2011). Advanced DBMS retrieved from aries.ektf.hu/~hz/pdf-tamop/pdf-xx/Radvanyi-
hdbms-eng2.pdf on December 13, 2017 at 15:06 PM

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