Types of Attributes
Simple attribute − Simple attributes are atomic values, which cannot be divided further. For example, a student's phone number is an atomic value of 10 digits.
Composite attribute − Composite attributes are made of more than one simple attribute. For example, a student's complete name may have first_name and last_name.
Derived attribute − Derived attributes are the attributes that do not exist in the physical database, but their values are derived from other attributes present in the database. For example, average_salary in a department should not be saved directly in the database, instead it can be derived. For another example, age can be derived from data_of_birth.
Single-value attribute − Single-value attributes contain single value. For example − Social_Security_Number.
Multi-value attribute − Multi-value attributes may contain more than one values. For example, a person can have more than one phone number, email_address, etc.
Key is an attribute or collection of attributes that uniquely identifies an entity among entity set.

The three-schema approach provides for three types of schemas with schema techniques based on formal language descriptions:
→External schema for user views
→Conceptual schema integrates external schemata
→Internal schema that defines physical storage structures

Functional Completeness Condition: It is the condition used to check the equivalence(The condition that all the data of the global relation must be mapped into the fragments) between global relation and its fragments after decomposition. When a relation is decomposed into fragments, both global relation and its fragments should be able to determine each other.
For decomposing a global relation, lossless decomposition is the necessary condition but functionally completeness problem is not a necessary condition.
A relation in BCNF may or may not be functionally complete

In database terms, a schema is the organisation and structure of a database. Both schemas and schemata can be used as plural forms. A schema contains schema objects, which could be tables, columns, data types, views, stored procedures, relationships, primary keys, foreign keys, etc.
A database schema can be represented in a visual diagram, which shows the database objects and their relationship with each other.