2. Schemas, sub schemas and instances
SCHEMAS –
It is the overall description or the overall design of the database
specified during the database design. Important thing to be
remembered here is it should not be changed frequently. Basically, it
displays the record types(entity),names of data items(attribute) but
not the relation among the files.
Interesting point is the values in schema might change but not the
structure of schema.
To understand it well, Schema can be assumed as a framework
where in the values of data items are to be fitted, these values can
be changed but not frame/format of the schema.
3. store_name store_id store_add city state zip_code
discount_type store_id lowqty highqty discount
STORES AND DISCOUNTS SCHEMAS
The former example shows the schema for stores displaying the name of the
store, store id, address, city and state in which it is located and the zip code of
respective location.
The latter example is all about schema of discounts that clearly shows the
type, id and quality, thus we can now relate to the fact that schema only
displays the record types (entities) and names of data items(attributes) but
does not show the relation among the files.
Schema can be partitioned as logical schema and physical schema.
5. Former part shows the logical schema which is concerned with the data structure with
exploring data structure offered to DBMS so that schema is very easy for the computer
to understand.
The latter part that is the physical schema is concerned with the way or the manner in
which conceptual database gets represented in the computer as it is stored in the
database.
Physical schema is hidden behind the logical schema and thus can be modified
without affecting the application programs
Database management system provides data definition language(DDL) and document
schema definition language(DSDL) to specify both logical and physical schema.
7. Instances
In simple words, it is the snapshot of the database taken at a particular moment. It can also be described
in more significant way as the collection of the information stored in the database at that particular
moment. Instance can also be called as the database state or current set of occurrence due the fact that it
is information that is present at the current state.
Every time we update the state say we insert, delete or modify the value of the data item in the record, it
changes from one state to other. At the given time, each schema has its own set of instances.
An organization with an employees database will have three different instances such as production that
is used to monitor the data right at that moment, per-production that is used to test new functionality
prior to release of production and the development that is used by database developers to create new
functionality.
An organization with an employees database will have three different instances such as production that
is used to monitor the data right at that moment, per-production that is used to test new functionality
prior to release of production and the development that is used by database developers to create new
functionality.
9. Roles and responsibilities of database
administrator
A database administrator, or DBA, is someone who is in charge of making
sure a database runs smoothly. As a challenging role that requires focus,
logic, and an enthusiastic personality that can cope under pressure, the job
necessitates a variety of skills. DBAs must work within an organization to
monitor, repair, and develop databases.
10. 1. Software Installation and Maintenance- A DBA is frequently involved in the initial installation
and configuration of a new Oracle, SQL Server, or other databases. The system administrator
configures the database server’s hardware and implements the operating system, after which the
DBA installs and configures the database software. The DBA is in charge of ongoing maintenance,
such as updates and patches. In addition, if a new server is implemented, the DBA is in charge of
transferring data from the existing system to the new platform.
2. Managing Data Integrity-DBAs primarily handle the overall integrity of a company’s database.
They make sure that the Data integrity is carefully managed because it protects data from
unauthorized use. DBAs manage data relationships to ensure data consistency.
3. Takes Care of Data Extraction, Transformation, and Loading- DBAs are responsible for Data
extraction, transformation, and loading, also known as (ETL), which refers to the efficient import of
large amount of data extracted from multiple systems into a data warehouse environment. The
external data is cleaned and transformed to fit the required format before being imported into a
central repository.
11. 4. Monitoring Performance- Only implementing a database is not the task of the
database administrator. Once the database is implemented, they are required to
monitor databases for performance issues. If a system component slows down
processing, the DBA may need to change the software configuration or add more
hardware capacity. There are numerous monitoring tools available, and
understanding what they need to track to improve the system is part of the DBA’s
job.
5. Data Handling- Each company’s success today revolves around massive
databases. Companies nowadays maintain massive databases containing
unstructured data types such as images, documents, or sound and video files.
Managing an extensive database (VLDB) may necessitate higher-level skills, as well
as additional monitoring and tuning, which a DBA possesses.
12. 6. Create a Database Backup Plan- DBAs create backup and recovery plans and procedures as per
the industry standards. Not only that, but DBAs make certain that all necessary steps are taken.
DBAs are responsible for ensuring that everything is completed on time, in addition to taking the
required precautions to keep data safe.
7. Database Recovery-The DBA’s responsibility in the event of a server failure or other type of data
loss is to restore lost data to the system using existing backups. Different types of failures may
necessitate different recovery strategies, and a DBA performs his duties while keeping the
necessary requirements in mind. Furthermore, as technology advances, it becomes crucial for a
DBA to backup databases to the cloud.
8. Database Security- One of the most critical responsibilities of a DBA is identifying and
correcting any flaws in the database software. No system is entirely secure; however, DBAs mitigate
risks by implementing best practices. A DBA must be able to identify potential flaws in the database
software and the overall system of the company and take appropriate steps to mitigate risks.
13. 9. Database Integrity-DBAs are primarily responsible for the overall integrity of a
company’s database. This includes putting the database in place, keeping it safe
from loss and corruption, making it easily accessible, ensuring it works properly, and
constantly tweaking it for ease of use and maximum productivity. In addition, the
database administrator is also in charge of training eligible employees on how to
access and use the database so that they can perform their duties.
10. Database Accessibility-Setting up employee access is a critical component of
database security. DBAs decide who has access and what kind of access they have.
They create a subschema to control database accessibility. They also determine
which users will have access to the database and which users will use data. Without
the permission of the DBA, no user has the authority to access the database.
14. 11. Provides Support to Users-If a user requires assistance at any time, it is the
DBA’s responsibility to assist him. The DBA provides complete support to users
who are new to the database.
12. Troubleshooting-In the event of a problem, DBA’s job is to troubleshoot it
immediately. Whether a DBA needs to quickly restore lost data or fix a problem
to limit damage, a DBA must be able to quickly understand and respond to
concerns when they occur.
16. A Database Architecture is a representation of DBMS design. It helps to
design, develop, implement, and maintain the database management
system. A DBMS architecture allows dividing the database system into
individual components that can be independently modified, changed,
replaced, and altered. It also helps to understand the components of a
database.
A Database stores critical information and helps access data quickly and
securely. Therefore, selecting the correct Architecture of DBMS helps in easy
and efficient data management.
17. Types of DBMS ARCHITECTURE
There are mainly three types of DBMS architecture:
1-Tier Architecture- 1 Tier Architecture in DBMS is the simplest architecture
of Database in which the client, server, and Database all reside on the same
machine. A simple one tier architecture example would be anytime you install a
Database in your system and access it to practice SQL queries. But such
architecture is rarely used in production.
18. 2-Tier Architecture- A 2 Tier Architecture in DBMS is a Database architecture
where the presentation layer runs on a client (PC, Mobile, Tablet, etc.), and data
is stored on a server called the second tier. Two tier architecture provides added
security to the DBMS as it is not exposed to the end-user directly. It also
provides direct and faster communication.
19. A 3 Tier Architecture in DBMS is the most popular client server architecture in DBMS in which
the development and maintenance of functional processes, logic, data access, data storage, and
user interface is done independently as separate modules. Three Tier architecture contains a
presentation layer, an application layer, and a database server.
3-Tier database Architecture design is an extension of the 2-tier client-server architecture. A 3-tier
architecture has the following layers:
1.Presentation layer (your PC, Tablet, Mobile, etc.)
2.Application layer (server)
3.Database Server
20. The Application layer resides between the user and the DBMS, which is
responsible for communicating the user’s request to the DBMS system and
send the response from the DBMS to the user. The application layer(business
logic layer) also processes functional logic, constraint, and rules before passing
data to the user or down to the DBMS.
The goal of Three Tier client-server architecture is:
•To separate the user applications and physical database
•To support DBMS characteristics
•Program-data independence
•Supporting multiple views of the data
21. Data Definition Language
Data Definition Language (DDL) is used to create and modify the structure of
objects in a database using predefined commands and a specific syntax. These
database objects include tables, sequences, locations, aliases, schemas and
indexes.
Commonly used DDL in SQL querying are CREATE, ALTER, DROP, and
TRUNCATE.
22. DDL is a standardized language with commands to define the storage groups (stogroups), different
structures and objects in a database. DDL statements create, modify and remove database objects, such
as tables, indexes and stogroups. DDL is also used in a generic sense to refer to any language that
describes data.
DDL includes Structured Query Language (SQL) statements to create and drop databases, aliases,
locations, indexes, tables and sequences. It also includes statements to alter these objects and impose or
drop certain constraints on tables, such as the following:
• UNIQUE
• PRIMARY
• FOREIGN KEY
• CHECK
These constraints are used to enforce uniqueness, referential or domain integrity.
23. Data Definition Language (DDL) is a subset of SQL. It is a language for describing data and its
relationships in a database.
• You can generate DDL in a script for database objects to: Keep a snapshot of the database
structure
• Set up a test system where the database acts like the production system but contains no data
• Produce templates for new objects that you can create based on existing ones. For example,
generate the DDL for the Customer table, then edit the DDL to create the table
Customer_New with the same schema.
When you generate DDL, you can use the DDL statements to recreate everything about a
database except for its contents. You can generate the DDL to completely recreate the
database, or choose to recreate only certain aspects of it, such as its current statistics. You
can also limit the statements that are generated so that only a segment of the database is
recreated, for example, the statistics for a subset of tables.
24. Data Manipulation Language (DML)
A DML (data manipulation language) refers to a computer programming language
that allows you to add (insert), delete (delete), and alter (update) data in a database.
A DML is typically a sublanguage of a larger database language like SQL, with the
DML containing some of the language’s operators. A DML (data manipulation
language) is a group of computer languages that provide commands for
manipulating data in databases.
The majority of SQL statements are categorised as DML (Data Manipulation
Language), which includes SQL commands that deal with modifying data in a
database. It’s the section of the SQL statement that controls who has access to the
database and data. DML statements and DCL statements are grouped together.
Because the DML command isn’t auto-committed, it won’t be able to save all
database changes permanently.
25. INSERT INTO Command
This command can be used to insert data into a row of a table. INSERT INTO would insert
the values that are mentioned in the ‘Student’ table below.
Syntax:
INSERT INTO NAME_OF_TABLE (1_column, 2_column, 3_column, …. N_column)
VALUES (1_value, 2_value, 3_value, …. N_value);
Or
INSERT INTO NAME_OF_TABLE
VALUES (1_value, 2_value, 3_value, …. N_value);
Example:
INSERT INTO Student(Stu_Name, DOB, Phone, Mail)
VALUES(‘Phoebe’, ‘1998-05-26’, 7812865845, ‘user@xyz.com’);
26. UPDATE Command
This statement in SQL is used to update the data that is present in an existing table of a database. The
UPDATE statement can be used to update single or multiple columns on the basis of our specific needs.
Syntax:
UPDATE name_of_table SET 1_coumn = 1_value, 2_coumn = 2_value, 3_coumn = 3_value, … , N_coumn =
N_value
WHERE condition;
And here,
name_of_table: name of the table
1_column, 2_column, 3_column, …. N_column: name of the first, second, third, …. nth column.
1_value, 2_value, 3_value, …. N_value: the new value for the first, second, third, …. nth column.
condition: the condition used to select those rows for which the column values need to be updated.
Example:
UPDATE Student SET Phone = 9039462901 WHERE Stu_Name = ’Phoebe’;
The WHERE clause in the preceding query is used to select the rows for which the columns need to be
adjusted, and the SET statement has been used to assign new values to a particular column. If the WHERE
clause is not used at all, then all of the rows’ columns will be modified. As a result, the WHERE clause is used
to pick specific rows from the table.
Thus, the example query would update the phone number of the student with the name ‘Phoebe’.
27. DELETE Command
The DELETE statement can be used in SQL to delete various records from a given table. On the
basis of the condition that has been set in the WHERE clause, one can delete single or multiple
records.
Syntax:
DELETE FROM name_of_table [WHERE condition];
Example:
DELETE FROM Student WHERE Stu_Name = ’Phoebe’;
The command given above would delete the record for the student with the name ‘Phoebe’
from the ‘Student’ table. Apart from this, one can also use the LOCK Table statement to explicitly
acquire the shared or exclusive table lock on a specified table.
29. The language which is used to create programs is called a programming language. It
comprises a set of instructions that are used to produce various kinds of output.
A fourth generation (programming) language (4GL) is a grouping of programming
languages that attempt to get closer than 3GLs to human language, form of thinking and
conceptualization.
4GLs are designed to reduce the overall time, effort and cost of software development. The
main domains and families of 4GLs are: database queries, report generators, data
manipulation, analysis and reporting, screen painters and generators, GUI creators,
mathematical optimization, web developmentand general purpose languages.
Also known as a 4th generation language, a domain specific language, or a high
productivity language.
30. Fourth-generation language (4GL), computer programming language that is
intended to be easier for users than machine languages (first-generation),
assembly languages (second-generation), and the older high-level languages
(third-generation). 4GLs are closer to human language than other high-level
languages and are accessible to people without formal training as programmers.
They allow multiple common operations to be performed with a single
programmer-entered command. 4GLs are usually not general-purpose languages
like third-generation languages such as C and C++ are but instead are usually
designed for a specific purpose, as in the case of SQL, which works with
databases.
31. Features of 4GL:
•It reduces programming costs and time.
•It is a high-level programming language.
•Its program has greater usability.
•It accesses the database.
•Minimum efforts from the user to obtain any
information.
Types of 4GL:
•Self-generator system.
•Report generator programming language.
•Form generators.
•Codeless programming.
•Data management.
32. Advantages of 4GL:
• Smaller in size as compared to the previous generation’s language.
• Graphics User Interface (GUI) technology was introduced.
• Low maintenance cost.
• The heat generated was negligible.
• Portable and cheaper than the previous generation.
33. Disadvantages of 4GL:
• Requires complex structure.
• The latest technology is required for the manufacturing of Microprocessors.
• Less flexible than other languages.
• Memory consumption is high.
![DELETE Command
The DELETE statement can be used in SQL to delete various records from a given table. On the
basis of the condition that has been set in the WHERE clause, one can delete single or multiple
records.
Syntax:
DELETE FROM name_of_table [WHERE condition];
Example:
DELETE FROM Student WHERE Stu_Name = ’Phoebe’;
The command given above would delete the record for the student with the name ‘Phoebe’
from the ‘Student’ table. Apart from this, one can also use the LOCK Table statement to explicitly
acquire the shared or exclusive table lock on a specified table.](https://image.slidesharecdn.com/unit2-250821172712-2085a5ce/85/UNIT-2-Database-Design-and-Languages-Schemas-sub-schemas-and-instances-27-320.jpg)
