What is Entity-Relation Ship Model ? or E-R Model ?

               Welcome To Series Articles of DBMS (volume-2)

Data model: It is known as the design of database management system, which can be used for the creation of a different kind of data model.

Types:

1)E-R model (entity-relationship model).
2)Relational model (Table).
3)Hirercial model.

1)E-R model: the basic requirement of the E-R model are the entity, attribute, and relationship.

E-R model consists of an entity and an attribute.

1.Entity: the real-world object which is having the physical existence. the pictorial representation of an entity is the rectangle.

Ex: 

2.Attribute: the description of the particular entity, which is known as a collection of different objects is identified as an attribute. The pictorial representation of attribute is oval.

Ex: 

Types of attributes: Simple attribute, Composite attribute, Multi-value attribute, Derived attribute. 

1.Simple attribute: it consists of a single value and it must be atomic.it cannot be further divided.

Ex: 

2.Composite attribute: when an attribute is derived it is known as a composite attribute. It can be further divided.

Ex:

3. Multi-value attribute: when an attribute has more than one value is known as a multi-value attribute. the pictorial representation of multi-value attribute is double oval.

Ex: A single person can have more than one phone number.

4. Derived attribute: if the attribute is derived from another attribute is known as a derived attribute. the pictorial representation of derived attribute is dotted oval.

Ex:  

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What is Data Base Management System ? What is SQL ?

Welcome To Series Articles of DBMS (volume-1)

In this article, you are going to get started with DBMS and an introduction to SQL.

Data: Raw fact or information which has real existence is known as Data.

Data Base: Collection of data or information in a particular area is known as database.

DBMS: All the data or information that is sequentially stored in DB and which can be retrieved from DB in according to the requirement of the user is known as Data Base Management System.

DBA: Data Base Administrator will control all the database transaction in the Data Base Management System.

SQL: SQL is a database computer language designed for the retrieval and management of data in a relational database.

DDL(Data Definition Language): DDL or Data Definition Language actually consists of the SQL commands that can be used to define the database schema. It simply deals with descriptions of the database schema and is used to create and modify the structure of database objects in the database.

Examples of DDL commands:

CREATE – is used to create the database or its objects (like table, index, function, views, store procedure and triggers).

DROP – is used to delete objects from the database.

ALTER-is used to alter the structure of the database.

TRUNCATE–is used to remove all records from a table, including all spaces allocated for the records are removed.

COMMENT –is used to add comments to the data dictionary.

RENAME –is used to rename an object existing in the database.

DML(Data Manipulation Language): The SQL commands that deals with the manipulation of data present in the database belong to DML or Data Manipulation Language and this includes most of the SQL statements.

Examples of DML:

SELECT – is used to retrieve data from the database.

INSERT – is used to insert data into a table.

UPDATE – is used to update existing data within a table.

DELETE – is used to delete records from a database table.

DCL(Data Control Language): DCL includes commands such as GRANT and REVOKE which mainly deals with the rights, permissions and other controls of the database system.

Examples of DCL commands:

GRANT-gives user’s access privileges to the database.

REVOKE-withdraw user’s access privileges given by using the GRANT command.

TCL(TransactionControl Language): TCL commands deals with the transaction within the database.

Examples of TCL commands: 

COMMIT– commits a Transaction. 

ROLLBACK– rollbacks a transaction in case of an error occurs. 

SAVEPOINT–sets a savepoint within a transaction. 

SET TRANSACTION–specify characteristics for the transaction.

Data Independence: A Database system normally contains a lot of data in addition to user data. It is rather difficult to modify or update a set of metadata once it is stored in the database. so that when we change data at one layer, it does not affect the data at another level. This data is independent but mapped to the physical level and logical level.

Physical data independence: the actual data is stored in the form of bits in the hard disk. Physical data independence is used to change the physical data without effecting logical data.

Logical data independence: It is a data about the database, it stores information about how the data is managed.

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I hope this article is useful to you, plz follow the next volume for more information.

You can write to me at codingallrounders@gmail.com

please post your doubts in the comment box.  

Indicate various properties of RAM, ROM, EPROM, EEPROM and FLASH memory.

Memory: memory is a storage area in the system.which usually store data and programs.almost every system needs a memory unit to store instructions of programs.

Classification of Memory:

Random Acess Memory (RAM):

It gets the word "random" because information can be accessed in non-sequential order. Though the
data itself is stored together, it could be anywhere in the "container" or amount of RAM available.
The microprocessor can Read the data from the RAM quickly faster than even from ROM. The microprocessor can write new data to the RAM quickly, erasing the old data in the RAM. The RAM forgets its data if the power is turned off.

Classification:

RAM is classified into two types Static RAM and Dynamic RAM.

Static RAM:
                     Static RAM retains data bits in its memory as long as power is being supplied. it remembers its data without any assistance from other parts of the circuit. the parts look like ROM parts expect that they have a write enable signal. it is a construction of circuits similar to D-flip flop. it is expensive and faster but generates more heat and consumes more power. it acts as a cache.

Dynamic RAM:
                          Dynamic RAM depends on being read once in a while otherwise it forgets its data. Systems employing dynamic RAM use a circuit called dynamic RAM refresh. it is a construction of tiny capacitors. it is inexpensive and uses less power but it is slower.it acts as main memory.

Comparison Table:

Read Only Memory (ROM):

The memory from which we can only read but cannot write on it. This type of memory is non-volatile. The information is stored permanently in such memories during manufacture. A ROM stores such instructions that are required to start a computer.

Programmable Read Only Memory (PROM):

It is Empty of data when manufactured but  Maybe permanently programmed by the user. The device programmer writes data to the device one word at a time by applying an electrical charge to the input pins of the chip. Once a PROM has been programmed in this way, its contents can never be

changed. If the code or data stored in the PROM must be changed, the current device must be discarded. As a result, PROMs are also known as one-time programmable (OTP) devices.

Erasable Programmable Read Only Memory (EPROM):

It can be programmed, erased and reprogrammed. the EPROM chip has a small window on top allowing it to be erased by shining ultra-violet light on it after reprogramming the window is covered to prevent new contents being erased. the access time is around 45 – 90 nanoseconds.

Electrically Erasable Programmable Read Only Memory (EEPROM):

It is Reprogrammed electrically without using ultraviolet light. it must be removed from the computer and placed in a special machine to do this. the access times between 45 and 200 nanoseconds.

Flash ROM:

 It is Similar to EEPROM however it can be reprogrammed while still on the computer. it is easier to upgrade programs stored in Flash ROM. it is used to store programs in devices e.g. modems. the access time is around 45 – 90 nanoseconds. it stores information in an array of memory cells.

I hope this article was successful in explaining you the basics of Memory.

You can write to me at codingallrounders@gmail.com

Define embedded systems? Discuss two examples for each Small, Medium and Large Scale Embedded Systems?

Embedded Systems:

An embedded system is a programmed controlling and operating system with a dedicated function within a larger mechanical or electrical system, often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts.

Embedded Systems Are classified into three types based on the performance of microcontroller they are Small Scall, Medium Scale, Large Scale Embedded Systems.

Small Scale Embedded Systems:

These types of embedded systems are designed with a single 8 or 16-bit microcontroller, that may even be activated by a battery. For developing embedded software for small-scale embedded systems, the main programming tools are an editor, assembler, cross assembler and integrated development environment (IDE).

Examples: Washing Machines, Security Alarms.


Medium Scale Embedded Systems:

These types of embedded systems design with a single or 16 or 32-bit microcontroller, RISCs or DSPs. These types of embedded systems have both hardware and software complexities. For developing embedded software for medium scale embedded systems, the main programming tools are C, C++, JAVA, Visual C++, RTOS, debugger, source code engineering tool, simulator, and IDE.

Examples: telecommunication, home Auto machine.


Large Scale Embedded Systems

These types of embedded systems have enormous hardware and software complexities, that may need ASIPs, IPs, PLAs, scalable or configurable processors. They are used for cutting-edge applications that need hardware and software Co-design and components which must assemble in the final system.

Examples: Set-top Boxes, Robotics.

I hope this article was successful in explaining you the basic classification of Embedded Systems.

You can write to me at codingallrounders@gmail.com