О a logically coherent structure (can be characterized as a whole). О some inherent meaning (represents some partial view of a portion of the real world). DataBase Management Systems Lecture Notes. UNIT Data: It is a collection of be stored in the DBMS and how it is likely to be used. The DBA creates the. Engineering Class handwritten notes, exam notes, previous year questions, PDF free download.

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This tutorial explains the basics of DBMS such as its architecture, data models, basic-to-advanced concepts related to Database Management Systems. A database-management system (DBMS) is a collection of interrelated data and a these goals the modeler must analyze narratives from users, notes from. DATABASE MANAGEMENT SYSTEMS. Tibor Radványi PhD. It was made with support of the TÁMOP/1/A

End users are the people whose jobs require access to the database for querying, updating, and generating reports; the database primarily exists for their use. There are several categories of end users: But they may need different information each time. Examples are bank-tellers or reservation clerks who do this activity for an entire shift of operations.

These include business analysts, scientists, engineers, others thoroughly familiar with the system capabilities. Many use tools in the form of software packages that work closely with the stored database. Mostly maintain personal databases using ready-to-use packaged applications.

An example is a tax program user that creates his or her own internal database. Describing data: The description of a database. Includes descriptions of the database structure and the constraints that should hold on the database. A diagrammatic display of some aspects of a database schema. The data in a DBMS is described at three levels of abstraction, as illustrated in the figure.

Defines DBMS schemas at three levels: Typically uses a physical data model. Uses a conceptual or an implementation data model.

Usually uses the same data model as pdfMachine - is a pdf writer that produces quality PDF files with ease! Data Base Management Systems 6 the conceptual level. The actual data stored in a database at a particular moment in time.

Also called database state or occurrence. Data Independence: When a schema at a lower level is changed, only the mappings between this schema and higher-level schemas need to be changed in a DBMS that fully supports data independence.

The higher-level schemas themselves are unchanged.

Codd IBM , first commercial system in Resulted in the IMS family of systems. The most popular model.

Other system based on this model: System 2k SAS inc. Most Recent Trend. Started with Informix Universal Server. The Entity Relationship ER data model allows us to describe the data involved in a real world enterprise in terms of objects and their relationships and is widely used to develop an initial data base design. Database design and ER Diagrams: The database design process can be divided into six steps.

The ER model is most relevant to the first three steps. Requirement Analysis: The very first step in designing a database application is to understand what data is to be stored in the database, what application must be built in top of it, and what operations are most frequent and subject to performance requirements. In other words, we must find out what the users want from the database. Conceptual database Design: The information gathered in the requirements analysis step is used to develop a high-level description of the data to be stored in the database, along with the constraints known to hold over this data.

The ER model is one of several high- level or semantic, data models used in database design. Logical Database Design: We must choose a database to convert the conceptual database design into a database schema in the data model of the chosen DBMS. Normally we will consider the Relational DBMS and therefore, the task in the logical design step is to convert an ER schema into a relational database schema.

Beyond ER Design 4. Schema Refinement: This step is to analyze the collection of relations in our relational database schema to identify potential problems, and refine it.

Physical Database Design: This step may simply involve building indexes on some table and clustering some tables or it may involve substantial redesign of parts of database schema obtained from the earlier steps.

Data Base Management Systems 9 6. Application and security Design: Any software project that involves a DBMS must consider aspects of the application that go beyond the database itself. We must describe the role of each entity users, user group, departments in every process that is reflected in some application task, as part of a complete workflow for the task.

Entity Types, Attributes and Keys: Entities are specific objects or things in the mini-world that are represented in the database.

Attributes are properties used to describe an entity. A specific entity will have a value for each of its attributes. Composite Attribute: Composition may form a hierarchy where some components are themselves composite. Single Valued Vs. Multi Valued: Phone number of an employee.

Stored Vs. Derived In some cases two are more attributes values are related — for example the age and date of birth of a person. The Age attribute is hence called a derived attribute and is said to be derivable from the Birthdate attribute , which is called stored attribute. Null Values In some cases a particular entity may not have an applicable value for an attribute.

For example, a college degree attribute applies only to persons with college degrees.

For such situation, a special value called null is created. Key attributes of an Entity Type: An important constraint on the entities of an entity type is the Key or uniqueness constraint on attributes. An entity type usually has an attribute whose values are distinct for pdfMachine - is a pdf writer that produces quality PDF files with ease! Data Base Management Systems 11 each individual entity in the entity set.

Such an attribute is called a Key attribute, and its values can be used to identify each entity uniquely. For example name attribute is a key of the company entity type, because no two companies are allowed to have the same name. In ER diagrammatic notation, each key attribute has its name underlined inside the oval.

Relationships and Relationship sets: A relationship is an association among two or more entities. For example we may have the relationship that Antony works in the Marketing department.

A relationship type R among the n entity types E1,E2,… ,En defines a set of associations or a relationship set- among entities from these entity types.

Informally each relationship instance ri in R is an association of entities, where the association includes exactly one entity from each participating entity type. Each such relationship instance ri represents the facts that the entities participating in ri are related in some way in the corresponding mini world situation.

Figure illustrates this example. Degree of a Relationship: The degree of a relationship is the number of participating entity types. A relationship type of degree two is called Binary, and one of degree three is called Ternary. An example of Ternary relationship is given below. Data Base Management Systems 12 Relationship of degree: Relationship types usually have certain constraints that limit the possible combinations of entities that may participate in the corresponding relationship set.

These constraints are determined from the mini world situation that the relationship represent. There are two type. Cardinality Ratio Describes maximum number of possible relationship occurrences for an entity participating in a given relationship type. Determines whether all or only some entity occurrences participate in a relationship. These are easy to specify for Binary Relationship Types. Data Base Management Systems 14 Example for 1: N relationships Alternative min, max notation for relationship structural constraints: Strong Entity a.

Entity which has a key attribute in its attribute list. Weak Entity a. Weak Entity Sets: An entity set that does not possess sufficient attributes to form a primary key is called a weak entity set. One that does have a primary key is called a strong entity set. For a weak entity set to be meaningful, it must be part of a one-to-many relationship set. This relationship set should have no descriptive attributes. A weak entity set does not have a primary key, but we need a means of distinguishing among the entities.

The discriminator of a weak entity set is a set of attributes that allows this distinction to be made. The primary key of a weak entity set is formed by taking the primary key of the strong entity set on which its existence depends see Mapping Constraints plus its discriminator.

To illustrate: It is existence-dependent on account. The primary key of a weak entity is found by taking the primary key of the strong entity on which it is existence- dependent, plus the discriminator of the weak entity set. It is a relationship between Strong entity and weak entity.

Data Base Management Systems 19 Specialization: Is the process of defining a set of subclasses of a super class. Attributes of a subclass are called specific attributes. Data Base Management Systems 20 We may have several specializations of the same super class Generalization: Attribute Defined: Disjointness Constraint: Completeness Constraint: Generalization usually is total because the super class is derived from the subclasses.

Relational Algebra: This property is called closure. One occurrence of each common attribute is eliminated from the result. Staff Staff. Based on use of tuple variables. Data Base Management Systems 39 - Ask questions about data in one or more tables. Data Base Management Systems 42 Chapter: Security Problems.

Describe the three levels of data abstraction? The are three levels of abstraction: 1. Physical level: The lowest level of abstraction describes how data are stored. Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data.

View level: The highest level of abstraction describes only part of entire database. Define the "integrity rules"? There are two Integrity rules. What is extension and intension? Extension: It is the number of tuples present in a table at any instance.


This is time dependent. Intension: It is a constant value that gives the name, structure of table and the constraints laid on it. What is System R? What are its two major subsystems? It is a prototype and its purpose was to demonstrate that it is possible to build a Relational System that can be used in a real life environment to solve real life problems, with performance at least comparable to that of existing system.

Its two subsystems are 1. Research Storage 2. System Relational Data System. How is the data structure of System R different from the relational structure? Unlike Relational systems in System R 1. Domains are not supported 2.

Enforcement of candidate key uniqueness is optional 3. Enforcement of entity integrity is optional 4. Referential integrity is not enforced.

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What is Data Independence? Data independence means that "the application is independent of the storage structure and access strategy of data". In other words, The ability to modify the schema definition in one level should not affect the schema definition in the next higher level.

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Two types of Data Independence: 1. Physical Data Independence: Modification in physical level should not affect the logical level. Logical Data Independence: Modification in logical level should affect the view level.

What is a view? How it is related to data independence?


A view may be thought of as a virtual table, that is, a table that does not really exist in its own right but is instead derived from one or more underlying base table. In other words, there is no stored file that direct represents the view instead a definition of view is stored in data dictionary. Growth and restructuring of base tables is not reflected in views. Thus the view can insulate users from the effects of restructuring and growth in the database.

Hence accounts for logical data independence. What is Data Model? A collection of conceptual tools for describing data, data relationships data semantics and constraints. What is E-R model? This data model is based on real world that consists of basic objects called entities and of relationship among these objects. Entities are described in a database by a set of attributes.

What is Object Oriented model? This model is based on collection of objects. An object contains values stored in instance variables with in the object. An object also contains bodies of code that operate on the object. These bodies of code are called methods.

Objects that contain same types of values and the same methods are grouped together into classes. What is an Entity? It is a 'thing' in the real world with an independent existence. What is an Entity type? It is a collection set of entities that have same attributes. What is an Entity set? It is a collection of all entities of particular entity type in the database.

What is an Extension of entity type? The collections of entities of a particular entity type are grouped together into an entity set. What is Weak Entity set? An entity set may not have sufficient attributes to form a primary key, and its primary key compromises of its partial key and primary key of its parent entity, then it is said to be Weak Entity set.

What is an attribute? It is a particular property, which describes the entity. What is a Relation Schema and a Relation?

Database Management System - DBMS Study Materials

A relation Schema denoted by R A1, A2, A relation is defined as a set of tuples. Let r be the relation which contains set tuples t1, t2, t3, What is degree of a Relation? It is the number of attribute of its relation schema. What is Relationship? It is an association among two or more entities. What is Relationship set? The collection or set of similar relationships. What is Relationship type? Relationship type defines a set of associations or a relationship set among a given set of entity types.

What is degree of Relationship type? It is the number of entity type participating. A data base schema is specifies by a set of definitions expressed by a special language called DDL. It specifies user views and their mappings to the conceptual schema. This language is to specify the internal schema. This language may specify the mapping between two schemas.

What is Data Storage - Definition Language? The storage structures and access methods used by database system are specified by a set of definition in a special type of DDL called data storage-definition language. This language that enable user to access or manipulate data as organised by appropriate data model. What is DML Compiler?

It translates DML statements in a query language into low-level instruction that the query evaluation engine can understand. What is Query evaluation engine? It executes low-level instruction generated by compiler.

What is DDL Interpreter? It interprets DDL statements and record them in tables containing metadata.


What is Record-at-a-time? This retrieve of a record is said to be Record-at-a-time. What is Set-at-a-time or Set-oriented? This retrieve of a record is said to be Set-at-a-time or Set-oriented. What is Relational Algebra? It is procedural query language.

It consists of a set of operations that take one or two relations as input and produce a new relation. What is Relational Calculus? It is an applied predicate calculus specifically tailored for relational databases proposed by E. How does Tuple-oriented relational calculus differ from domain-oriented relational calculus? The tuple-oriented calculus uses a tuple variables i.

QUEL 2. The domain-oriented calculus has domain variables i. What is normalization? It is a process of analysing the given relation schemas based on their Functional Dependencies FDs and primary key to achieve the properties 1. Minimizing redundancy, 2. Minimizing insertion, deletion and update anomalies.

What is Functional Dependency? A Functional dependency is denoted by X Y between two sets of attributes X and Y that are subsets of R specifies a constraint on the possible tuple that can form a relation state r of R. This means the value of X component of a tuple uniquely determines the value of component Y. What is Lossless join property? It guarantees that the spurious tuple generation does not occur with respect to relation schemas after decomposition.

What is 1 NF Normal Form? The domain of attribute must include only atomic simple, indivisible values. What is Fully Functional dependency? It is based on concept of full functional dependency. A functional dependency X Y is full functional dependency if removal of any attribute A from X means that the dependency does not hold any more.

What is 2NF? What is 3NF? X is a Super-key of R. A is a prime attribute of R. In other words, if every non prime attribute is non-transitively dependent on primary key. What is 4NF?

X is a super key. What is 5NF? The join dependency is implied by the set of FD, over R in which the left side is key of R. What is Domain-Key Normal Form? A relation is said to be in DKNF if all constraints and dependencies that should hold on the the constraint can be enforced by simply enforcing the domain constraint and key constraint on the relation.

What are partial, alternate,, artificial, compound and natural key? Partial Key: It is a set of attributes that can uniquely identify weak entities and that are related to same owner entity.

It is sometime called as Discriminator. Artificial Key: If no obvious key, either stand alone or compound is available, then the last resort is to simply create a key, by assigning a unique number to each record or occurrence. Then this is known as developing an artificial key.What is Domain-Key Normal Form? Physical Database Design: This damage can occur when your computer crashes, a virus infects, you accidentally reformat a disk that contains precious data, or you experience some other catastrophe of considerable dimension.

SQL commands are instructions used to communicate with the database to perform specific task that work with data. This model is based on collection of objects. Concurrent access is not possible.

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