Q.1) Describe Three Levels of Data Abstraction?Ans. For Understanding : (1. Physical level : how the data is stored physically and where it is stored indatabase.2. Logical level : what information or data is stored in the database (like what is thedatatype or what is format of data.3.View level : end users work on view level. if any amendment is made it can besaved by other name. )1. The major purpose of a database system is to provide users with anabstract viewof the system.The system hides certain details of how data is stored and created and maintainedComplexity should be hidden from database users.Data abstraction is a process of representing the essential features withoutincluding implementation details.many database-systems users are not computer trained, developers hide thecomplexity from users through several levels of abstraction, to simplify usersinteractions with the system:

1) Physical level.The lowest level of abstraction describes how the data areactually stored. The physical level describes complex low-level datastructures in detail. E.g. index, B-tree, hashing.

2) Logical level.The next-higher level of abstraction describes what data arestored in the database, and what relationships exist among those data. Thelogical level thus describes the entire database in terms of a small number ofrelatively simple structures.

3) View level.The highest level of abstraction describes only part of the entiredatabase. The variety of information stored in a large database. Many usersof the database system do not need all this information; instead, they needto access only a part of the database. The view level of abstraction exists tosimplify their interaction with the system. E.g. tellers in a bank get a view of customer accounts, but not of payroll data.Q.2) What is Data Abstraction?Ans.Abstraction, in general, is the process of taking away or removing characteristics from something in order to reduce it to a set of essential characteristics. As in abstract art, the representation is likely to be one potential abstraction of a number of possibilities. Adatabase abstraction layer, for example, is one of a number of such possibilities.Data abstraction is usually the first step in database design. A completedatabaseis much too complex a system to be developed without first creating a simplified framework. Data abstraction makes it possible for the developer to start from essential elements -- data abstractions -- and incrementally add data detail to create the final system. Example: A doctor sees (abstracts) thepersonas patient. The doctor is interested in name, height, weight, age, blood group, previous or existing diseases etc of a person An employer sees (abstracts) apersonas Employee. The employer is interested in name, age, health, degree of study, work experience etc of a person.

Q.3) Define the term Data Independence?Ans.Data Independence:Data independenceis the type ofdatatransparency that matters for a centralizedDBMS. It refers to the immunity of userapplicationsto changes made in the definition and organization of data.There's a lot of data in whole database management system other than user's data. DBMS comprises of three kinds of schemas, which is in turn data about data (Meta-Data). Meta-data is also stored along with database, which once stored is then hard to modify. But as DBMS expands, it needs to be changed over the time satisfy the requirements of users. But if the whole data were highly dependent it would become tedious and highly complex.

[Image: Data independence]Data about data itself is divided in layered architecture so that when we change data at one layer it does not affect the data layered at different level. This data is independent but mapped on each other.Logical Data IndependenceLogical data is data about database, that is, it stores information about how data is managed inside. For example, a table (relation) stored in the database and all constraints, which are applied on that relation.Logical data independence is a kind of mechanism, which liberalizes itself from actual data stored on the disk. If we do some changes on table format it should not change the data residing on disk.Physical Data IndependenceAll schemas are logical and actual data is stored in bit format on the disk. Physical data independence is the power to change the physical data without impacting the schema or logical data.For example, in case we want to change or upgrade the storage system itself, that is, using SSD instead of Hard-disks should not have any impact on logical data or schemas.

Q.4) Define an entity, entity set , relationship and relationship set?Ans.Entity :An entity is a person,place,thing or event for which data is collected and maintained.for example...a library system may contain data about different entities like BOOK and MEMBER.A college system may include entities like STUDENT,TEACHER and CLASS...

Entity Set: Anentity setis a set of entities of the same type (e.g., all persons having an account at a bank). Entity setsneed not be disjoint. For example, the entity setemployee(all employees of a bank) and the entity setcustomer(all customers of the bank) may have members in common. An entity is represented by a set ofattributes. E.g. name, S.I.N., street, city for ``customer'' entity. Thedomainof the attribute is the set of permitted values (e.g. the telephone number must be seven positive integers). Formally, an attribute is afunctionwhich maps an entity set into a domain. Every entity is described by a set of (attribute, data value) pairs. There is one pair for each attribute of the entity set. E.g. a particularcustomerentity is described by the set {(name, Harris), (S.I.N., 890-123-456), (street, North), (city, Georgetown)}.An analogy can be made with the programming language notion of type definition. The concept of anentity setcorresponds to the programming languagetype definition. A variable of a given type has a particular value at a point in time. Thus, a programming language variable corresponds to anentityin the E-R model.

Relationships & Relationship SetsArelationshipis an association between several entities.Arelationship setis a set of relationships of the same type.Formallyit is a mathematical relation on(possibly non-distinct) sets.Ifare entity sets, then a relationship set R is asubsetof

whereis a relationship.For example, consider the two entity setscustomerandaccount. (Fig. 2.1 in the text). We define the relationshipCustAcctto denote the association between customers and their accounts. This is abinaryrelationship set (see Figure 2.2 in the text).Going back to our formal definition, the relationship setCustAcctis a subset of all the possible customer and account pairings.This is a binary relationship. Occasionally there are relationships involving more than two entity sets.Theroleof an entity is the function it plays in a relationship. For example, the relationshipworks-forcould be ordered pairs ofemployeeentities. The first employee takes the role of manager, and the second one will take the role of worker.A relationship may also havedescriptiveattributes. For example,date(last date of account access) could be an attribute of theCustAcctrelationship set.

Q.5) What are the different types of database system users?Ans1. Application programmers or Ordinary users2. End users3. Database Administrator (DBA) 4. System Analyst1. Application programmers or Ordinary users: These users write application programs to interact with the database. Application programs can be written in some programming language such a COBOL, PL/I, C++, JAVA or some higher level fourth generation language. Such programs access the database by issuing the appropriate request, typically a SQL statement to DBMS.2. End Users:End users are the users, who use the applications developed. End users need not know about the working, database design, the access mechanism etc. They just use the system to get their task done. End users are of two types:a) Direct users b) Indirect usersa) Direct users:Direct users are the users who se the computer, database system directly, by following instructions provided in the user interface. They interact using the application programs already developed, for getting the desired result. E.g. People at railway reservation counters, who directly interact with database.b) Indirect users:Indirect users are those users, who desire benefit form the work of DBMS indirectly. They use the outputs generated by the programs, for decision making or any other purpose. They are just concerned with the output and are not bothered about the programming part.3.Database Administrator (DBA):Database Administrator (DBA) is the person which makes the strategic and policy decisions regarding the data of the enterprise, and who provide the necessary technical support for implementing these decisions. Therefore, DBA is responsible for overall control of the system at a technical level. In database environment, the primary resource is the database itself and the secondary resource is the DBMS and related software administering these resources is the responsibility of the Database Administrator (DBA).4. System Analyst:System Analyst determines the requirement of end users, especially nave and parametric end users and develops specifications for transactions that meet these requirements. System Analyst plays a major role in database design, its properties; the structure prepares the system requirement statement, which involves the feasibility aspect, economic aspect, technical aspect etc. of the system.Q.6) Define Simple , composite attributes and single valued and multivalued attributes?AnsSingle and Composite AttributesAttributes can be classified as having many parts to them or just a single unbreakable attribute. The composite attribute is an attribute that can be subdivided into other single attributes with meanings of their own. A single attribute is just an attribute that cannot be subdivided into parts.Example: Imagine from the entityStudentthat instead of having the three attributes:stu_LastName, stu_MiddleName, stu_FirstNameit had one attribute calledstu_Name. The attributestu_Namewould be considered a composite attribute since it can be subdivided into the other three attributes:stu_LastName, stu_MiddleName, stu_FirstName. The rest of attributes would be consider single attributes since they can't be subdivided into parts.

Single-valued and multi-valued AttributesAttributes can be classified as single or multi value. The single-value attribute can only have one value, while the multi-valued attributes usually can store multiple data in them.Example: In the entityStudent,stu_Addresscould be considered a multi-value attribute since a student could have multiple addresses where he lives at. An example of a single-value attribute would bestu_LastNamesince a student usually has one last name that uniquely identifies him/her.Q.7) Explain Derived Attribute with example?AnsThe last category that attributes can be defined is called a derived attribute, where one attribute is calculated from another attribute. The derived attribute may not be stored in the database but rather calculated using algorithm.Example: In the entityStudent,stu_Agewould be considered a derived attribute since it could be calculated using the student's date of birth with the current date to find their age.examples of derived attributes are:salary,age or DOB.Q.8) What is total and partial participation?AnsTotal participationEvery member of entity set must participate in the relationship Represented bydouble linefrom entity rectangle to relationship diamond E.g., AClassentity cannot exist unless related to aFacultymember entity in this example, not necessarily at Juniata. You can set this double line in Dia In a relational model we will use thereferencesclause.

Partial Participation: Thereexistan instance of the first entity type that dont share an instance of the relationshiptype withthe other entity type.

Q.9) Define Primary key , Candidate key and Super Key?AnsAprimary keyis a column (or columns) in a table that uniquely identifies the rows in that table.CUSTOMERSCustomerNoFirstNameLastName

1SallyThompson

2SallyHenderson

3HarryHenderson

4SandraWellington

For example, in the table above, CustomerNo is the primary key.The values placed in primary key columns must be unique for each row: no duplicates can be tolerated. In addition, nulls are not allowed in primary key columns.Definition:A candidate key is a combination of attributes that can be uniquely used to identify a database record without any extraneous data. Each table may have one or more candidatekeys. One of these candidate keys is selected as the tableprimary key.Definition:A superkey is a combination of attributes that can be uniquely used to identify a database record. A table might have many superkeys.Candidate keysare a special subset of superkeys that do not have any extraneous information in them.Examples:Imagine a table with the fields , , and . This table has many possible superkeys. Three of these are , and . Of those listed, only is a candidate key, as the others contain information not necessary to uniquely identify records.Q.10) What is Weak Entity set and Strong Entity Set?AnsWEAK ENTITY SETWeak entity set may not have sufficient attributes to form a primary key.Eg:An entity set payment with the following attributes:payment-number,payment-date and payment-amount.STRONG ENTITY SETStrong entity setis an entity set that has a primary key.Eg:An entity set customer with the following attributes:customer-name,customer-id and balance.Q.11) Distinguish Between Specialization And Generalization?Ansgeneralization and specialization are important relationships that exist betweena higher level entity set and one or more lower level entity sets.1. generalization is the result of taking the union of two or more lower level entity sets to produce a higher level entity sets.specialization is the results of taking subsets of a higher level entity set to form a lower level entity sets.2. In generalization,each higher level entity must also be a lower level entity.

In specialization,some higher level entities may not have lower-level entity sets at all.3. Specialization is aTop Downprocess where as Generalization isBottom Upprocess.Q.12) What is Aggregation?Ans. Aggregation refers to performing an operation on a group of values to get a single result. One limitation of the E-R model is that it cannot express relationships among the relationships so to overcome this we use aggregation. Aggregation is a process when the relation between two entity is treated as a single entity. Aggregation represents abstract entities by allowing relationship between relationships. Aggregation is a special type of Association. Aggregation is also called a "Has-a" relationship.UML Notation:

Example

5 Marks Q.1) Compare database systems with file systems.

Database Systems

File Systems

Data are non-redundant and consistent

Data are redundant and inconsistent

Easy to access the data

Difficult to access the data

It ensures integrity, security and atomicity

It doesnt ensure integrity, security and atomicity

Data can be accessed concurrently

It leads to concurrent access anomalies

Appropriate data can be retrieved easily

Since data is scattered in various files,new application programs have to be written to retrieve the appropriate data

Q.2) Define and map E R Model to Relational Model?AnsEntity-Relationship ModelEntity-Relationship model is based on the notion of real world entities and relationship among them. While formulating real-world scenario into database model, ER Model creates entity set, relationship set, general attributes and constraints.ER Model is best used for the conceptual design of database.ER Model is based on: Entitiesand theirattributes Relationshipsamong entitiesThese concepts are explained below.

[Image: ER Model] EntityAn entity in ER Model is real world entity, which has some properties calledattributes. Every attribute is defined by its set of values, calleddomain.For example, in a school database, a student is considered as an entity. Student has various attributes like name, age and class etc. RelationshipThe logical association among entities is calledrelationship. 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 manyConverting (Mapping) E-R Model to Relational Model E-R Model -> Relational Model -> Normalization -> Database Previously, we covered modeling the users view as an E-R diagram. Entities, Relationships, Attributes and Identifiers. We now need to convert this conceptual representation to a model that can be implemented directly in a database. Relational Model includes:Relations, Tuples, Attributes, keys and foreign keys. Relation: A two dimensional table make up of tuples (This is a simple definition that we will define more rigorously in a later chapter). Tuple: A row of data in a relation made up of one or more attributes. Attribute: A characteristic of the relation contained in a tuple.The following are some vocabulary that are commonly used. Note the different terms used depending on the model being discussed.ER ModelRelational ModelDatabaseTraditional Programmer

EntityRelationTableFile

Entity InstanceTupleRowRecord

AttributeAttributeColumnField

IdentifierKeyKeyKey (or link)

Q.3) What is relational algebra ? Describe any three operations with eg?AnsRelational 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 operationsOperators 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.Terminology Relation - a set of tuples. Tuple - a collection of attributes which describe some real world entity. Attribute - a real world role played by a named domain. Domain - a set of atomic values. Set - a mathematical definition for a collection of objects which contains no duplicates.Select Operation ()Selects tuples that satisfy the given predicate from a relation.Notation p(r)Wherepstands for selection predicate and r stands for relation.pis prepositional logic formulae which may use connectors like and, or and not. These terms may use relational operators like: =,,,< , >, .For example:subject="database"(Books)Output : Selects tuples from books where subject is 'database'.subject="database" and price="450"(Books)Output : Selects tuples from books where subject is 'database' and 'price' is 450.subject="database" and price < "450" or year > "2010"(Books)Output : Selects tuples from books where subject is 'database' and 'price' is 450 or the publication year is greater than 2010, that is published after 2010.Project Operation ()Projects column(s) that satisfy given predicate.Notation: A1, A2, An(r)Where a1, a2, anare attribute names of relation r.Duplicate rows are automatically eliminated, as relation is a set.for example: subject, author (Books)Selects and projects columns named as subject and author from relation Books.Union Operation ()Union operation performs binary union between two given relations and is defined as: r s = { t | t r or t s} Notion: r U sWhere r and s are either database relations or relation result set (temporary relation).For a union operation to be valid, the following conditions must hold: r, s must have same number of attributes. Attribute domains must be compatible.Duplicate tuples are automatically eliminated. author (Books) author (Articles) Output : Projects the name of author who has either written a book or an article or both.

Q.4) Explain EER Features?Ans

Attribute inheritanceThe attributes of higher level entity set are inherited by lower level entity set.AggregationAggregation is an abstraction in which relationship sets are treated as higher level entity sets. Here a relationship set is embedded inside an entity set, and these entity sets can participate in relationships.

Q.7) Explain Join Operation of Relational Algebra?AnsFrom Korth book Q.8) Write a queries on relational algebra?Ans1. Consider a database with the following schema:

Person( name, age, gender )name is a key

Frequents( name, pizzeria )(name, pizzeria) is a key

Eats( name, pizza )(name, pizza) is a key

Serves( pizzeria, pizza, price )(pizzeria, pizza) is a key

Write relational algebra expressions for the following nine queries. (Warning: some of the later queries are a bit challenging.)

If you know SQL, you can try running SQL queries to match your relational algebra expressions. We've created afile for downloadwith schema declarations and sample data. (See ourquick guidefor SQL system instructions.) To check your queries, the correct results are found in the answers section below.

a.Find all pizzerias frequented by at least one person under the age of 18.

b.Find the names of all females who eat either mushroom or pepperoni pizza (or both).

c.Find the names of all females who eat both mushroom and pepperoni pizza.

d.Find all pizzerias that serve at least one pizza that Amy eats for less than $10.00.

e.Find all pizzerias that are frequented by only females or only males.

f.For each person, find all pizzas the person eats that are not served by any pizzeria the person frequents. Return all such person (name) / pizza pairs.

g.Find the names of all people who frequent only pizzerias serving at least one pizza they eat.

h.Find the names of all people who frequent every pizzeria serving at least one pizza they eat.

i.Find the pizzeria serving the cheapest pepperoni pizza. In the case of ties, return all of the cheapest-pepperoni pizzerias.

2. Consider a schema with two relations,R(A, B) andS(B, C), where all values are integers. Make no assumptions about keys. Consider the following three relational algebra expressions:Two of the three expressions are equivalent (i.e., produce the same answer on all databases), while one of them can produce a different answer. Which query can produce a different answer? Give the simplest database instance you can think of where a different answer is produced.

3. Consider a relationR(A, B) that contains r tuples, and a relationS(B, C) that contains s tuples; assume r>0 and s>0. Make no assumptions about keys. For each of the following relational algebra expressions, state in terms of r and s the minimum and maximum number of tuples that could be in the result of the expression.4. Two more exotic relational algebra operators we didn't cover are thesemijoinandantijoin. Semijoin is the same as natural join, except only attributes of the first relation are returned in the result. For example, if we have relationsStudent(ID, name) andEnrolled(ID, course), and not all students are enrolled in courses, then the query "StudentEnrolled" returns the ID and name of all students who are enrolled in at least one course. In the general case, E1E2returns all tuples in the result of expression E1such that there is at least one tuple in the result of E2with matching values for the shared attributes. Antijoin is the converse: E1E2retuns all tuples in the result of expression E1such that there are no tuples in the result of E2with matching values for the shared attributes. For example, the query "StudentEnrolled" returns the ID and name of all students who are not enrolled in any courses.

Like some other relational operators (e.g., intersection, natural join), semijoin and antijoin are abbreviations - they can be defined in terms of other relational operators. Define E1E2in terms of other relational operators. That is, give an equation "E1E2=??", where ?? on the right-hand side is a relational algebra expression that doesn't use semijoin. Similarly, give an equation "E1E2=??", where ?? on the right-hand side is a relational algebra expression that doesn't use antijoin.

5. Consider a relationTemp(regionID, name, high, low) that records historical high and low temperatures for various regions. Regions have names, but they are identified by regionID, which is a key. Consider the following query, which uses the linear notation introduced at the end of the relational algebra videos.State in English what is computed as the final Result. The answer can be articulated in a single phrase.

1. Sample solutions; in general there are many correct expressions for each query.Query results for SQL data:a.Straw Hat, New York Pizza, Pizza Hut

b.Amy, Fay

c.Amy

d.Little Caesars, Straw Hat, New York Pizza

e.Little Caesars, Chicago Pizza, New York Pizza

f.Amy: mushroom, Dan: mushroom, Gus: mushroom

g.Amy, Ben, Dan, Eli, Fay, Gus, Hil

h.Fay

i.Straw Hat, New York Pizza

2. Query (c) is different. LetR= {(3, 4)} andS= {(1, 2)}. Then query (a) and (b) produce an empty result while (c) produces {(3, 2)}.

3.a. Minimum = max(r, s) (if one relation is a subset of the other) Maximum = r + s (if the relations are disjoint)

b. Minimum = 0 (if there are no shared B values) Maximum = r x s (if all of the B values are the same)

c. Minimum = 0 (if there are no shared B values) Maximum = min(r, s) (if one relation's B values are a subset of the other's, and all B values are distinct)

d. (equivalent to R) Minimum = r, Maximum = r

e. Minimum = 0 (if A = B in all tuples ofR) Maximum = r (if A B in all tuples ofR)

4.5. Names of regions with the highest high temperature and/or lowest low temperature

https://www.classle.net/book/dbms