Database System Concepts: Chapter 2 Outline Quiz

Data Models, Schemas, and Instances

• Data abstraction: suppression of details of data organization and storage, highlighting essential features for improved understanding of data.
• Data model: a collection of concepts that describe the structure of a database, providing means to achieve data abstraction.
• Basic operations: specify retrievals and updates on the database, allowing the database designer to specify a set of valid operations allowed on database objects.

Categories of Data Models

• High-level or conceptual data models: close to the way many users perceive data.
• Low-level or physical data models: describe the details of how data is stored on computer storage media.
• Representational data models: easily understood by end users, similar to how data is organized in computer storage.
• Entity: represents a real-world object or concept.
• Attribute: represents some property of interest, further describing an entity.
• Relationship: represents an association among entities.
• Entity-Relationship model: describes entities and relationships.

Schemas, Instances, and Database State

• Database schema: description of a database.
• Schema diagram: displays selected aspects of the schema.
• Schema construct: each object in the schema.
• Database state or snapshot: data in the database at a particular moment in time.
• Define a new database: specify the database schema to the DBMS, initial state, and valid state.
• Schema evolution: changes applied to the schema as application requirements change.

Three-Schema Architecture and Data Independence

• Internal level: describes the physical storage structure of the database.
• Conceptual level: describes the structure of the whole database for a community of users.
• External or view level: describes part of the database that a particular user group is interested in.
• Data independence: capacity to change the schema at one level of a database system without having to change the schema at the next higher level.
• Logical data independence: changes to the conceptual schema do not affect the external schema.
• Physical data independence: changes to the internal schema do not affect the conceptual schema.

Database Languages

• Data definition language (DDL): defines schemas.
• Storage definition language (SDL): specifies the internal schema.
• View definition language (VDL): specifies user views/mappings to conceptual schema.
• Data manipulation language (DML): allows retrieval, insertion, deletion, and modification.
• High-level or nonprocedural DML: can be used on its own to specify complex database operations concisely.
• Low-level or procedural DML: must be embedded in a general-purpose programming language.

The Database System Environment

• DBMS component modules: buffer management, stored data manager, DDL compiler, interactive query interface, query compiler, query optimizer, and precompiler.
• Runtime database processor: executes queries and updating commands.
• System catalog: stores metadata about the database.
• Concurrency control system: manages concurrent access to the database.
• Backup and recovery system: provides backup and recovery capabilities.

Database System Utilities

• Loading: load existing data files into the database.
• Backup: creates a backup copy of the database.
• Database storage reorganization: reorganize a set of database files into different file organizations.
• Performance monitoring: monitors database usage and provides statistics to the DBA.

Centralized and Client/Server Architectures for DBMSs

• Centralized DBMSs architecture: all DBMS functionality, application program execution, and user interface processing carried out on one machine.
• Client/Server architecture: separates the functionality into clients and servers.
• Two-Tier Client/Server Architectures: client handles user interface programs and application programs, server handles query and transaction functionality related to SQL processing.
• Three-Tier and n-Tier Architectures: adds intermediate layers between the client and the database server.

Classification of Database Management Systems

• Data model: Relational, Object, Hierarchical and network (legacy), Native XML DBMS.
• Number of users: Single-user, Multiuser.
• Number of sites: Centralized, Distributed, Homogeneous, Heterogeneous.
• Cost: Open source, Different types of licensing.
• Access path options: general or special-purpose.