2. Database System Concepts and Architecture Flashcards
client module
runs on user workstation or personal computer (handles user interaction and provides user-friendly interfaces)
server module
Handles data storage, access, search etc.
client/server DBMS architecture
system functionality is distributed between two types of modules
data model
a collection of concepts that can be used to describe the structure of a database
high-level / conceptual data model
close to user perception of data
low-level / physical data model
describe details of how data is stored
entity
a real-world object or concept that is described in the database
representational / implementation data models
provide concepts that may be understood by end users but that are not too far removed from the way data is organized within the computer
attribute
some property of interest that further describes an entity
relationship
an association among two or more entities
access path
structure that makes the search for particular database records efficient
object data models
higher-level implementation data model that are closer to conceptual data models
database schema
description of a database (during design, does not change often)
schema diagram
displayed schema with schema constructs (no instances)
database state or snapshot / current set of occurrences or instances
the data in the database at a particular moment in time
valid state
a state that satisfies the structure and constraints specified in the schema
meta-data
descriptions of the schema constructs and constraints
intension of a database
the database schema
extension of schema
database state
three-schame architecture (goal)
separate user applications and physical database
internal level / internal schema
describes physical structure of database
conceptual level / conceptual schema
describes structure of whole database for community of users
external or view level
includes number of external schemas or user views
mappings
process of transforming requests and results between levels
levels of three-schema architecture
- internal 2. conceptual 3. external
operating system (OS)
system that controls access to database disk (with stored data manager module)
stored data manager module
carry out low-level data transfer between disk and computer main storage (sometimes buffer handling)
buffer manager module
module for handling buffering of disk pages
DDL compiler
processes schema definitions and stores meta-data in DBMS catalog
Runtime database processor
handles database accesses at runtime (retrieves and carries out retrieval or update operations)
Query compiler
handles high-level queries
precompiler
extracts DML commands from an application program (in host programming language)
DML compiler
compiles DML commands into object code for database access
host language compiler
compiles the rest of the program (without DML commands)
client/server architecture
deal with environments with large number of PCs, workstations, file servers etc connected via a network
specialized servers
e.g. file server, printer server, web server, e-mail server
client machines
provide user with appropriate interfaces to utilize these servers
client
a user machine that provides user interface capabilities and local processing
server
a machine that can provide services to the client machines (file access, printing, archiving, database access)
Two-tier architectures
software components are distributed over two systems: client and server
advantage two-tier
simplicity and seamless compatibility with existing systems
middle tier, application server, Web server
Plays intermediate role by storing business rules that are used to access data from the database server
What are the three tiers
user interface, application rules, data access
