CH 2 Database System Concepts and Architecture

Question 1

Define data model

Answer 1

• A data model—a collection of concepts that can be used to describe the structure of a database like data type, relationships, and constraints that apply to the data basic operations for specifying retrievals and updates on the database
• Types: relational, object, object-relational, NOSQL, key-value, hierarchical, network, and other.

Question 2

Define database schema

Answer 2

• The description of a database is called the
  database schema
• Contrast: The schema does not change very often, whereas the database state changes every time data is inserted, deleted, or modified. T

Question 3

Define host language

Answer 3

Wheneever DML commands, whether high level or low level, are embedded in a general-purpose programming language, that language is called the host language

• Not SQL
• Examples: Java

Question 4

Describe the three-schema architecture. Why do we need mappings among schema levels? How do different schema definition languages support this architecture?

Answer 4

• A DBMS divided in internal schema (physical storage), conceptual schema (data model), external schema (user view)
• A DBMS that cleanly separates the three levels must have mappings among the schemas to transform requests and query results from one level to the next.

Question 5

2.2 Discuss the main categories of data models. What are the basic differences among the relational model, the object model, and the XML model?

Answer 5

three main categories:
■ High-level or conceptual data models (based on entities and relationships). use concepts such as entities, attributes, and relationships. ER, EER
■ Low-level or physical data models. how data is stored on the computer storage media
■ Representational or implementation data models (record-based, object- oriented). relational
data model (SQL), the network and hierarchical models. represent data by using record structures.
- Relational data model is SQL
- Object model: high-level conceptual models, 
- XML: self-describing data models. The data storage in systems based on these models combines the description of the data with the data values

Question 6

2.5. What is the difference between logical data independence and physical data independence? Which one is harder to achieve? Why?

Answer 6

• Logical data independence is the capacity to change the conceptual schema without having to change external schemas or application programs.
• Physical data independence is the capacity to change the internal schema without having to change the conceptual schema. H
• Logical is harder

Question 7

2.6. What is the difference between procedural and nonprocedural DMLs?

Answer 7

• A high-level or nonprocedural DML can be used on its own to specify complex database operations concisely.. Example: SQL, Which data to retrieve rather than how to retrieve it; therefore, such languages are also called declarative.
• A low- level or procedural DML must be embedded in a general-purpose programming language. retrieves individual records . Therefore, it needs to use programming language constructs, such as looping,

Question 8

2.9. What is the difference between the two-tier and three-tier client/server architectures?

Answer 8

• two-tier architectures because the soft- ware components are distributed over two systems: client and server. query and transac- tion functionality related to SQL processing remained on the server side. The user interface programs and application programs can run on the client side.
• Client, web server, data base server. Web server intermediary role by running application programs and storing business rules (procedures or con- straints) that are used to access data from the database server