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

Classification of Database Management Systems

2.1. Define the following terms: data model, database schema, database state,
internal schema, conceptual schema, external schema, data independence,
DDL, DML, SDL, VDL, query language, host language, data sublanguage,
database utility, catalog, client/server architecture, three-tier architecture,
and n-tier architecture.
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?
2.3. What is the difference between a database schema and a database state?
2.4. Describe the three-schema architecture. Why do we need mappings among
schema levels? How do different schema definition languages support this
architecture?
2.5. What is the difference between logical data independence and physical data
independence? Which one is harder to achieve? Why?
2.6. What is the difference between procedural and nonprocedural DMLs?
2.7. Discuss the different types of user-friendly interfaces and the types of users
who typically use each.
2.8. With what other computer system software does a DBMS interact?
2.9. What is the difference between the two-tier and three-tier client/server
architectures?
2.10. Discuss some types of database utilities and tools and their functions.
2.11. What is the additional functionality incorporated in n-tier architecture
(n . 3)?

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