T S I: Logical schema L: Views II: Physical schema M: File organization and indexes III: External schema N: Relations
Which one of the following is the correct match from T to S ?
DBMS Schema Matching: Solution
This question requires matching the different levels of database schema abstraction (External, Logical, Physical) with their corresponding components within a DBMS context.
Understanding Database Schema Levels
Database schemas define the structure of a database at different levels of abstraction:
- External Schema (View Level): Describes the part of the database relevant to a particular user or application. It hides certain details of the database.
- Logical Schema (Conceptual Level): Defines the overall structure of the database, including entities, attributes, relationships, and constraints, independent of physical storage details.
- Physical Schema (Internal Level): Describes how the data is actually stored on the storage devices. It deals with file organization, indexing, and other low-level details.
Matching Schemas to Concepts
We need to match the items in set T (I, II, III) with the items in set S (L, M, N).
- I: Logical schema corresponds to Relations (N). The logical schema is primarily concerned with the structure of tables (relations), their columns (attributes), and the relationships between them.
- II: Physical schema corresponds to File organization and indexes (M). The physical schema deals with how data is stored in files and how indexes are used to speed up data retrieval.
- III: External schema corresponds to Views (L). Views provide a specific perspective or subset of the data defined in the logical schema, representing the external schema for users.
Therefore, the correct matching is:
- I – N
- II – M
- III – L
This corresponds to Option C.
Important Questions from ER Model
______ are some problems that can occur when creating an entity-relationship model.
The values of the attributes in a database describe a particular _______.
Which of the following data item is not broken down into smaller units is?
Which of the following statements is/are TRUE?
(i) A weak entity set is identified solely by its partial key (discriminator).
(ii) The identifying relationship type between a weak entity type and its owner entity type must have total participation from the weak entity type.
- Consider an ER model with the entities E1(A11, A12, A13) and E2(A21, A22, A23), where, A11, A12, A13 are the attributes of E1, and A21, A22, A23 are the attributes of E2. Let A22 be a multi-valued attribute. A11 and A21 are the primary keys of E1 and E2, respectively.
Let R12 be a many-to-many relationship between E1 and E2. Participation of both E1 and E2 in R12 is total.
The minimum number of relations required to convert the ER model into relational model (assuming there is no other functional dependency) where each relation is in third normal form (3NF) is __________ . (Answer in integer)
