Data independence refers to the ability to modify either the conceptual or internal schema without requiring changes to the other. There are two types of data independence: physical data independence, which allows changes to the physical storage structure without affecting the conceptual schema, and logical data independence, which allows changes to the conceptual schema without affecting external schemas. An entity-relationship model uses entities, attributes, and relationships to graphically represent how data is organized within a database. Entities can have simple, composite, derived, single-value, or multi-value attributes, and keys uniquely identify entities within an entity set.

1. Data Independence
- Software application must not be
changed when changes occur in data definition.
2 kinds of Data Independence
Physical Data Independence
- indicates that the physical storage
structure or devices could be change without
affecting conceptual schema. The changed
would be absorbed by the mapping between the
conceptual and internal level.

2. Logical Data Independence
- indicates that the conceptual schema
can be changed without affecting the existing
external schemas. The change would be
absorbed by the mapping between the
external and conceptual levels.
*For example: consider two users A & B.
Both are selecting the empno and ename. If user
B add a new column salary in his view/table then
it will not effect the external view user; user A, but
internal view of database has been changed for
both users A & B. Now user A can also print the
salary.

3. Data
- In general, data is any set of characters that
has been gathered and translated for some
purpose, usually analysis. It can be any
character, including text and numbers, pictures,
sound, or video. If data is not put into context, it
doesn't do anything to a human or computer.
- Within a computer's storage, data is a
collection of numbers represented
as bytes that are in turn composed
of bits (binary digits) that can have the value
one or zero. Data is processed by the CPU,
which uses logical operations to produce new
data (output) from source data (input).

4. Database Languages and
Interface
 Database Languages
- DDL for describing data and data structures a
suitable description tool, a data definition
language (DDL), is needed. With this help a
data scheme can be defined and also changed
later.
Typical DDL operations (with their respective
keywords in the structured query
language SQL):
- Creation of tables and definition of
attributes (CREATE TABLE ...)
- Change of tables by adding or deleting
attributes (ALTER TABLE …)
- Deletion of whole table including content
(!) (DROP TABLE …)

5. - DML additionally a language for the descriptions
of the operations with data like store, search, read,
change, etc. the so-called data manipulation, is
needed. Such operations can be done with a data
manipulation language (DML). Typical DML
operations (with their respective keywords in the
structured query language SQL):
- Add data (INSERT)
- Change data (UPDATE)
- Delete data (DELETE)
- Query data (SELECT)
*Often these two languages for the definition and
manipulation of database are combined in one
comprehensive language. A good example is the
Structured Query Language (SQL).

6. Database Interface
 Working Principle of Database Interface
The application poses with the help of SQL, a
query language, a query to the database system. There,
the corresponding answer (result set) is prepared and
also with the help of SQL given back to the application.
This communication can take place interactively or be
embedded into another language.

7.  Type and Use of Database Interface
1. Interactive
- SQL can be used interactively from
a terminal.
2. Embedded
- SQL can be embedded into
another language (host language)
which might be used to create a
database application.

8. Data Modeling Using the
Entity-Relationship
Model

9. Entity-Relationship (ER)Model
- an entity-relationship model, also
called an Entity-Relationship (ER)
diagram, is a graphical representation
of Entity and their Relationship to each
other, typically used in computing in
regard to the organization of data
within databases or information
systems.

11. Entity and Attributes
Entity
- an entity can be a real world object,
either animate or inanimate, that can be
easily identifiable.
*Example
In a school database; students,
teachers, classes and courses
offered.
All these entities have some attributes or
properties that give them their identity.

12. - an entity set is a collection of similar
types of entities. An entity set may
contain entities with attribute sharing
similar value.
*Example
- a Students set may contain all the
students of a school.
- a Teacher set may contain all the
teachers of a school from all faculties.

13. Entity Type/Entity set
Entity Type (Intension): STUDENT
Attributes: Name, Age,
Address
Entity Set (Extension):e1 = (John Smith,
16,
Antipolo City)
e2 = (Joe Doe, 40,
Manila)
e3 = (Jane Doe, 27,
Taytay)

14. Entity and Attributes
 Attributes
- entities are represented by means of
their properties, called attributes. All
attributes have values.
*Example
- Student entity may have name,
age and address as attributes.

15. - There exists a domain or range of
values that can be assigned to
attributes.
*Example
- a student’s name cannot be a
numeric value, it has to be alphabetic.
- a student’s age cannot be
negative, etc.

16. Types of Attributes
 Simple Attributes
- simple attributes are atomic values, which
cannot be divided further.
*Example
-Student’s phone number is an atomic value
of 7 digits.
 Composite Attributes
- composite attributes are made of more than
one simple attribute.
*Example
- Student’s complete name may have
First_name and Last_name

17. Types of Attributes
 Derived Attribute
- are the attributes that do not exist in the physical
database, but their values are derived from other
attributes present in the database.
*Example
Age can be derived from date_of_birth
 Single-value Attribute
- single-value attributes contain single value.
*Example : SSS number
 Multi-value Attribute
- may contain more than one values.
*Example : Phone number, email address

18. Entity Set and Keys
 Key – is an attribute or collection of
attributes that uniquely identifies an
entity among entity set.
*Example
- the id_number of a student makes
him/her identifiable among students.