Master of Computer Application (MCA) – Semester 2

MC0067 – Database Management System

(DBMS and Oracle 9i)

Assignment Set – 1

1. Explain the functions and advantages of a DBMS over a traditional file system.

Ans:- A DBMS is a set of software programs that controls the organization, storage, management, and retrieval of data in a database. DBMSs are categorized according to their data structures or types. The DBMS accepts requests for data from an application program and instructs the operating system to transfer the appropriate data. The queries and responses must be submitted and received according to a format that conforms to one or more applicable protocols. When a DBMS is used, information systems can be changed more easily as the organization's information requirements change. New categories of data can be added to the database without disruption to the existing system.

advantages of a DBMS:-

• Management of distributed data with different levels of transparency.• Increase reliability and availability.• Easier expansion.• Reflects organizational structure — database fragments are located in the departments

they relate to.• Local autonomy — a department can control the data about them (as they are the ones

familiar with it.)• Protection of valuable data — if there were ever a catastrophic event such as a fire, all

of the data would not be in one place, but distributed in multiple locations.• Improved performance — data is located near the site of greatest demand, and the

database systems themselves are parallelized, allowing load on the databases to be balanced among servers. (A high load on one module of the database won't affect other modules of the database in a distributed database.)

• Economics — it costs less to create a network of smaller computers with the power of a single large computer.

• Modularity — systems can be modified, added and removed from the distributed database without affecting other modules (systems).

• Reliable transactions - Due to replication of database.• Hardware, Operating System, Network, Fragmentation, DBMS, Replication and

Location Independence.• Continuous operation.

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2. Describe indexing and clustering techniques with relevant real time examples.

Ans:- The most important characteristics of column data are the clustering factor for the column

and the selectivity of column values, even though other important characteristics within tables are

available to the CBO. A column called clustering_factor in the dba_indexes view offers information

on how the table rows are synchronized with the index. When the clustering factor is close to the

number of data blocks and the column value is not row ordered when the clustering_factor

approaches the number of rows in the table, the table rows are synchronized with the index.

To illustrate this, the following query will filter the result set using a column value for clustering_factor:

select customer_name from customer where customer_state = ‘New Mexico’;

An index scan is faster for this query if the percentage of customers in New Mexico is small and the values are clustered on the data blocks. The decision to use an index versus a full-table scan is at least partially determined by the percentage of customers in New Mexico.So, why would a CBO choose to perform a full-table scan when only a small number of rows are retrieved? The clustering_factor has the answer. Four factors synchronize to help the CBO choose whether to use an index or a full-table scan: the selectivity of a column value; the db_block_size ; the avg_row_len ; and the cardinality. An index scan is usually faster if a data column has high selectivity and a low clustering_factor.

3. Describe various integrity rules with a relevant example.

Ans:- It is important that data adhere to a predefined set of rules, as determined by the

database administrator or application developer. As an example of data integrity, consider

the tables employees and departments and the business rules for the information in each

of the tables.

Types of Data Integrity

This section describes the rules that can be applied to table columns to enforce different types of data integrity.

Null Rule

A null is a rule defined on a single column that allows or disallows inserts or updates of rows containing a null (the absence of a value) in that column.

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Unique Column Values

A unique value defined on a column (or set of columns) allows the insert or update of a row only if it contains a unique value in that column (or set of columns).

Primary Key Values

A primary key value defined on a key (a column or set of columns) specifies that each row in the table can be uniquely identified by the values in the key.

Referential Integrity Rules

A rule defined on a key (a column or set of columns) in one table that guarantees that the values in that key match the values in a key in a related table (the referenced value).Referential integrity also includes the rules that dictate what types of data manipulation are allowed on referenced values and how these actions affect dependent values. The rules associated with referential integrity are:

• Restrict: Disallows the update or deletion of referenced data.• Set to Null: When referenced data is updated or deleted, all associated dependent data is set to

NULL.• Set to Default: When referenced data is updated or deleted, all associated dependent data is set

to a default value.• Cascade: When referenced data is updated, all associated dependent data is correspondingly

updated. When a referenced row is deleted, all associated dependent rows are deleted.

Complex Integrity Checking

Complex integrity checking is a user-defined rule for a column (or set of columns) that allows or disallows inserts, updates, or deletes of a row based on the value it contains for the column (or set of columns).

Integrity Constraints Description

An integrity constraint is a declarative method of defining a rule for a column of a table. Oracle supports the following integrity constraints:

• NOT NULL constraints for the rules associated with nulls in a column• UNIQUE key constraints for the rule associated with unique column values• PRIMARY KEY constraints for the rule associated with primary identification values• FOREIGN KEY constraints for the rules associated with referential integrity. Oracle supports the

use of FOREIGN KEY integrity constraints to define the referential integrity actions, including: o Update and delete No Actiono Delete CASCADEo Delete SET NULL

4. Explain the three-level architecture of a DBMS with a labeled diagram.

Ans:- Data are actually stored as bits, or numbers and strings, but it is difficult to work with data at this level.

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It is necessary to view data at different levels of abstraction.

Schema:

• Description of data at some level. Each level has its own schema.

We will be concerned with three forms of schemas:

• physical, • conceptual, and • external.

5. Describe the relational algebra operations with relevant real time examples.

Ans:- n order to implement a DBMS, there must exist a set of rules which state how the database system will behave. For instance, somewhere in the DBMS must be a set of statements which indicate than when someone inserts data into a row of a relation, it has the effect which the user expects. One way to specify this is to use words to write an `essay' as to how the DBMS will operate, but words tend to be imprecise and open to interpretation. Instead, relational databases are more usually defined using Relational Algebra.

Relational Algebra is :

• the formal description of how a relational database operates • an interface to the data stored in the database itself • the mathematics which underpin SQL operations

Operators in relational algebra are not necessarily the same as SQL operators, even if they have the same name. For example, the SELECT statement exists in SQL, and also exists in relational algebra. These two uses of SELECT are not the same. The DBMS must take whatever SQL statements the user types in and translate them into relational algebra operations before applying them to the database.

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More formally, R × S is defined as follows:

R × S = {(r1, r2, ..., rn, s1, s2, ..., sm) | (r1, r2, ..., rn) ∈ R, (s1, s2, ..., sm) ∈ S}

More formally the semantics of the natural join is defined as follows:

More formally the semantics of the semijoin is defined as follows:

R S = { t : t R, s S, Fun (t s) }

6. Write about the database system environment.

Ans:- Database Management System (DBMS) is a set of computer programs that controls the

creation, maintenance, and the use of a database. It allows organizations to place control of database

development in the hands of database administrators (DBAs) and other specialists. A DBMS is a

system software package that helps the use of integrated collection of data records and files known

as databases. It allows different user application programs to easily access the same database.

DBMSs may use any of a variety of database models, such as the network model or relational

model. In large systems, a DBMS allows users and other software to store and retrieve data in a

structured way. Instead of having to write computer programs to extract information, user can ask

simple questions in a query language. Thus, many DBMS packages provide Fourth-generation

programming language (4GLs) and other application development features. It helps to specify the

logical organization for a database and access and use the information within a database. It provides

facilities for controlling data access, enforcing data integrity, managing concurrency, and restoring

the database from backups. A DBMS also provides the ability to logically present database

information to users.

7. Describe Entity Types, Entity Sets, Attributes and Keys.

Ans:-

Entity Types & Sets:- An entity is a term from the entity-relationship model.A relational model (your database schema) is one of the ways to implement the ER model.Relational tables represent relations between simple types like integers and strings, which, in their turn, can represent everything: entities, attributes, relationships.

• An entity is any object in the system that we want to model and store information about • Individual objects are called entities • Groups of the same type of objects are called entity types or entity sets • Entities are represented by rectangles (either with round or square corners)

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Attribute:-

• All the data relating to an entity is held in its attributes. • An attribute is a property of an entity. • Each attribute can have any value from its domain. • Each entity within an entity type:

o May have any number of attributes. o Can have different attribute values than that in any other entity. o Have the same number of attributes.

• Attributes can be • simple or composite • single-valued or multi-valued • Attributes can be shown on ER models • They appear inside ovals and are attached to their entity. • Note that entity types can have a large number of attributes... If all are shown then the

diagrams would be confusing. Only show an attribute if it adds information to the ER diagram, or clarifies a point.

8. Explain the following database operations with one query example for each:

a) Insert:-insert statements have the following form:

• INSERT INTO table (column1, [column2, ... ]) VALUES (value1, [value2, ...])

The number of columns and values must be the same. If a column is not specified, the default value for the column is used. The values specified (or implied) by the INSERT statement must satisfy all the applicable constraints (such as primary keys, CHECK constraints, and NOT NULL constraints). If a syntax error occurs or if any constraints are violated, the new row is not added to the table and an error returned instead.

Example:

INSERT INTO phone_book (name, number) VALUES ('John Doe', '555-1212');

b) Delete:- The DELETE statement follows the syntax:

DELETE FROM table_name [WHERE condition]

Any rows that match the WHERE condition will be removed from the table. If the WHERE clause is omitted, all rows in the table are removed. The DELETE statement does not return any rows; that is, it will not generate a result set.

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Executing a DELETE statement can cause triggers to run that can cause deletes in other tables. For example, if two tables are linked by a foreign key and rows in the referenced table are deleted, then it is common that rows in the referencing table would also have to be deleted to maintain referential integrity.

Delete rows from mytable using a subquery in the where condition:

DELETE FROM mytable WHERE id IN (SELECT id FROM mytable2);

c) Update:- An SQL UPDATE statement changes the data of one or more records in a table. Either all the rows can be updated, or a subset may be chosen using a condition.

The UPDATE statement has the following form:

UPDATE table_name SET column_name = value [, column_name = value ...] [WHERE condition]

For the UPDATE to be successful, the user must have data manipulation privileges (UPDATE privilege) on the table or column, the updated value must not conflict with all the applicable constraints (such as primary keys, unique indexes, CHECK constraints, and NOT NULL constraints).

Set the value of column C1 in table T to 1, only in those rows where the value of column C2 is "a".

UPDATE T SET C1 = 1 WHERE C2 = 'a';

August 2010

Master of Computer Application (MCA) – Semester 2

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MC0067 – Database Management System

(DBMS and Oracle 9i)

Assignment Set – 2

1. Describe the following normalization techniques:

a)Third Normal Form:- The normal forms (abbrev. NF) of relational database theory provide criteria for determining a table's degree of vulnerability to logical inconsistencies and anomalies. The higher the normal form applicable to a table, the less vulnerable it is to inconsistencies and anomalies. Each table has a "highest normal form" (HNF): by definition, a table always meets the requirements of its HNF and of all normal forms lower than its HNF; also by definition, a table fails to meet the requirements of any normal form higher than its HNF.

The normal forms are applicable to individual tables; to say that an entire database is in normal form n is to say that all of its tables are in normal form.Every non-prime attribute is non-transitively dependent on every candidate key in the table.

b)Boyce-Codd Normal Form:- Newcomers to database design sometimes suppose that

normalization proceeds in an iterative fashion, i.e. a 1NF design is first normalized to 2NF, then to 3NF,

and so on. This is not an accurate description of how normalization typically works. A sensibly designed

table is likely to be in 3NF on the first attempt; furthermore, if it is 3NF, it is overwhelmingly likely to

have an HNF of 5NF. Achieving the "higher" normal forms (above 3NF) does not usually require an

extra expenditure of effort on the part of the designer, because 3NF tables usually need no modification

to meet the requirements of these higher normal forms. Every non-trivial functional dependency in

the table is a dependency on a superkey.

2. Describe the theory of Discretionary Access control based on granting and revoking

privileges.

Ans:- Discretionary access control is based on the idea of access rights, or privileges, and mechanisms for giving users such privileges. A privilege allows a user to access some data object in a certain manner (e.g. to read or modify). A user who creates data object such as a table or a view automatically gets all applicable privileges on that object and the user can also propagate privileges using "Grant Option". The DBMS subsequently keeps track of how these privileges are granted to other users, and possibly revoked, and ensures that at all times only users with the necessary privileges can access an object.

SQL Syntax

SQL supports discretionary access control through the GRANT and REVOKE commands.

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The GRANT command gives users privileges to base tables and views.

The REVOKE command cancels uses' privileges.

For example: GRANT privilege1, privilege2, ... ROVOKE privilege1, privilege2, ... ON object_name ON object_name TO user1, user2, ... ; FROM user1, user2, ... ; GRANT SELECT, ALTER ROVOKE SELECT, ATLER ON student ON student TO db2_14 FROM db2_14

3. Write about Encryption and Public Key Infrastructures.

Ans:- Encryption Algorithm:-

Input: encryption key K (one key for the entire database), a

page of plaintext values (P bytes), and a randompermutation (function) associated with the page (one foreach page) perm :{1,.., P}→{1,.., P}.Output: a page of ciphertext values.We consider and encrypt each byte of the page separately:For i = 1to P,(1) Let d perm(i) mod | K | i = which is clearly in the range

of [0, |K|-1].

Public Key Infrastructure (PKI) is a set of hardware, software, people, policies, and procedures needed to create, manage, distribute, use, store, and revoke digital certificates.[1] In cryptography, a PKI is an arrangement that binds public keys with respective user identities by means of a certificate authority (CA). The user identity must be unique within each CA domain. The binding is established through the registration and issuance process, which, depending on the level of assurance the binding has, may be carried out by software at a CA, or under human supervision. The PKI role that assures this binding is called the Registration Authority (RA). For each user, the user identity, the public key, their binding, validity conditions and other attributes are made unforgettable in public key certificates issued by the CA.

The term trusted third party (TTP) may also be used for certificate authority (CA). The term PKI is sometimes erroneously used to denote public key algorithms, which do not require the use of a CA.

4. Describe the categories of Informix Universal Server.

Ans:- This used to be where I'd let off steam after uncovering a nasty bug in the Illustra object-relational database management system. And, in fact, sometimes I reached such poetic heights

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of vitriol that I'm leaving the old stuff at the bottom (also, it might be useful if you are still running Illustra for some reason).

However, there really aren't any good reasons to pick on Illustra anymore. The company was bought by Informix, one of the "big three" traditional RDBMS vendors (Oracle and Sybase being the other two). Informix basically folded the interesting features of the old Illustra system into their industrial-strength enterprise-scale RDBMS and calls the result "Informix Universal Server" (IUS). To the extent that IUS is based on old code, it is based on Informix's tried and true Online Server, which has been keeping banks and insurance companies with thousands of simultaneous users up and running for many years.

I plan to be experimenting with IUS in some heavily accessed sites during the latter portion of 1997. I'm going to record my experiences here and hope to have lots of tips and source code to distribute.

5. Describe the following concepts in the context of Joins:

a. Keys :- A key is an attribute (also known as column or field) or a combination of attribute that is

used to identify records. The purpose of the key is to bind data together across tables without repeating

all of the data in every table.

(I) Super Key – An attribute or a combination of attribute that is used to identify the records uniquely is

known as Super Key. A table can have many Super Keys.

(II) Candidate Key – It can be defined as minimal Super Key or irreducible Super Key. In other words an

attribute or a combination of attribute that identifies the record uniquely but none of its proper subsets can identify

the records uniquely.

(III) Primary Key – A Candidate Key that is used by the database designer for unique identification of each

row in a table is known as Primary Key. A Primary Key can consist of one or more attributes of a table.

(IV) Foreign Key – A foreign key is an attribute or combination of attribute in one base table that points to the

candidate key (generally it is the primary key) of another table. The purpose of the foreign key is to ensure

referential integrity of the data i.e. only values that are supposed to appear in the database are permitted.

(V) Composite Key – If we use multiple attributes to create a Primary Key then that Primary Key is called

Composite Key.

(VI) Alternate Key – Alternate Key can be any of the Candidate Keys except for the Primary Key.

(VII) Secondary Key – The attributes that are not even the Super Key but can be still used for identification

of records (not unique) are known as Secondary Key.

b. Performing a Join :- A SQL JOIN clause combines records from two or more tables in a database.[1] It creates a set that can be saved as a table or used as is. A JOIN is a means for combining

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fields from two tables by using values common to each. ANSI standard SQL specifies four types of JOINs: INNER, OUTER, LEFT, and RIGHT. In special cases, a table (base table, view, or joined table) can JOIN to itself in a self-join.A programmer writes a JOIN predicate to identify the records for joining. If the evaluated predicate is true, the combined record is then produced in the expected format, a record set or a temporary table.

All subsequent explanations on join types in this article make use of the following two tables. The rows in these tables serve to illustrate the effect of different types of joins and join-predicates. In the following tables the DepartmentID column of the Department table (which can be designated as Department.DepartmentID) is the primary key, while Employee.DepartmentID is a foreign key.

c. Distinct and Eliminating Duplicates:- every field in one record is identical to every field in a different record, i.e. a duplicate is where there is no way of telling two or more records apart. If you just need to remove records which are similar (i.e. one or more fields are identical but there are one or more fields which are different) then instead refer to how to delete similar records.

To check that you have duplicate records in your table do the following:

select count(*) from MyTable

and

select distinct * from MyTable

Unfortunately there is no way in SQL to delete one of these duplicates without deleting all of them. They are identical after all, so there is no SQL query that you could put together which could distinguish between them.

What you can do is to copy all the distinct records into a new table:

select distinct *into NewTablefrom MyTable

This query will create a new table (NewTable in my example) containing all the records in the original table but without any records being duplicated. It will therefore preserve a single copy of those records which were duplicated.

6. Explain the E-R to relational mapping with a suitable example.

Ans:- For each regular entity type E in the ER schema,– create a relation R that includes all the simple attributesof E– include only simple component attributes of compositeattribute– choose one of the key attributes of E as primary keyfor R• Ex. Employee, Department, Project relations– primary key :

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• Employee(SSN), Department(DNUMBER),Project(PNUMBER.

Upon completion of this module, you will be introduced to the following

The use of high-level conceptual data models to support database design. The basic concepts associated with the Entity–Relationship (ER) model, a high-level

conceptual data model. A diagrammatic technique for displaying an ER model. How to identify problems called connection traps, which may occur when creating an

ER model. The limitations of the basic ER modeling concepts and the requirements to model more

complex applications using enhanced data modeling concepts. The main concepts associated with the Enhanced Entity–Relationship (EER) model

called specialization/generalization and categorization.

7. Describe the Concurrency Control Techniques in a DBMS.

Ans:- Concurrency control in Database management systems (DBMS; Bernstein et al. 1987, Weikum and Vossen 2001), other transactional objects, and related distributed applications (e.g., Grid computing and Cloud computing) ensures that database transactions are performed concurrently without violating the data integrity of the respective databases. Thus concurrency control is an essential element for correctness in any system where two database transactions or more, executed with time overlap, can access the same data, e.g., virtually in any general-purpose database system. A well established concurrency control theory exists for database systems: serializability theory, which allows to effectively design and analyze concurrency control methods and mechanisms.

To ensure correctness, A DBMS usually guarantees that only serializable transaction schedules are generated, unless serializability is intentionally relaxed. For maintaining correctness in cases of failed (aborted) transactions (which can always happen for many reasons) schedules also need to have the recoverability property. A DBMS also guarantees that no effect of committed transactions is lost, and no effect of aborted (rolled back) transactions remains in the related database. Overall transaction characterization is usually summarized by the following ACID rules.

8. Explain the following with respect to files:

a) Sorted Files:- Many alternatives exist, each with its strengthsand weaknesses:Heap (random order) files: Suitable when typicalaccess is a file scan retrieving all records.Sorted Files: Best if records must be retrieved insome order, or only a `range’ of records is needed.Indexes: Data structures to organize records viatrees or hashing.Like sorted files, they speed up searches for a subset ofrecords, based on values in certain (“search key”) fieldsUpdates are much faster than in sorted files.

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b) Heap Files:- Rows are simply appended to the end of the file as they are inserted. Hence the file is unordered.

Deleted rows will create gaps in file. File then must be periodically compacted to recover space.

Heap File – Performance:-

Inserting a row:

• Access path is to append to the end• Retrieve and store one page

Updating a row:

• Access path is to scan whole file• Avg. F/2 page transfers if row already exists• F+1 page transfers if row does not already exist

Deleting a row:

• Access path is scan• Avg. F/2+1 page transfers if row exists• F page transfers if row does not exist

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