Elweven by four
DATABASE MANAGEMENT
DBMS can control user access at the following levels:
DBMS can include a data dictionary that identifies the fields, their characteristics and their use.
DBMS software aids in organizing, controlling and using the data needed by application programs.
DBMS provides the facility to create and maintain a
well-organized database
Primary functions include reduced data redundancy,
decreased access time and basic security over sensitive data
• User and the database
• Program and the database
• Transaction and the database
• Program and data field
• User and transaction
• User and data field
advantages of a DBMS include:
• Data independence for application systems
• Ease of support and flexibility in meeting changing data requirements
• Transaction processing efficiency
• Reduction of data redundancy
• Ability to maximize data consistency
• Ability to minimize maintenance cost through data sharing
• Opportunity to enforce data/programming standards
• Opportunity to enforce data security
• Availability of stored data integrity checks
• Facilitation of terminal users’ ad hoc access to data, especially through designed query language/application generators
DBMS ARCHITECTURE
Data Dictionary/Directory System
three types of metadata:
Within each level, there is a data definition language (DDL) component for creating the schema representation necessary for interpreting and responding to the user’s request.
internal schema
external schema
DBMS will typically accommodate multiple DDLs for several application programming languages compatible with the DBMS.
conceptual schema,
will provide appropriate
mappings between the external and internal schemas.
includes data about data elements used to define logical and physical fields, files, data relationships, queries
Data elements required to define a database are called metadata.
helps define and store source and object forms of all data definitions for external schemas, conceptual schemas, the internal schema and all associated mappings.
contains an index and description of all the items stored in the
database.
location of the data and the access
method.
DD/DS provides the following functional capabilities:
• A data definition language processor, which allows the database administrator to create or modify a data definition for mappings between external and conceptual schemas
• Validation of the definition provided to ensure the integrity of the metadata
• Prevention of unauthorized access to, or manipulation of, the metadata
• Interrogation and reporting facilities that allow the DBA to make inquiries on the data definition
Some of the benefits of using DD/DS include:
• Enhance documentation.
• Provide common validation criteria.
• Facilitate programming by reducing the needs for data definition.
• Standardize programming methods.
DATABASE STRUCTURE
three major types of database structure
hierarchical
network
relational
is a hierarchy of parent
and child data segments
this model uses
parent-child relationships
(one-to-many) mappings between
record types represented by logical trees,
data relationships are hierarchical, the database is easy to
implement, modify and search
registry in Microsoft Windows is an
example of a hierarchical database
basic data modeling
construct is called a set
set is formed by
a member
record type
a name
owner record type
can have that role in more than one set, so a multiowner relationship is allowed
can also be a member or owner in another set
disadvantage of the network model is that such structures can be extremely complex and difficult to comprehend, modify or reconstruct in case of failure.
definition of data structures, storage/retrieval operations and integrity constraints.
In such adatabase, the data and relationships among these data are organized in tables.
table is a collection of rows, also known as tuples, and each tuple in a table contains the same columns
Relational databases are used in most common ERP Systems.
Columns, called domains or attributes,
correspond to fields
Tuples are equal to records in a conventional file
structure
Relational tables have the following properties:
• Values are atomic, i.e., a single unit that is irreducible
• Each row is uniquely identifiable.
• Column values are of the same kind.
• The sequence of columns is insignificant.
• The sequence of rows is insignificant.
• Each column has a unique name.
relational model is independent from the physical implementation of the data structure and has many advantages over the hierarchical and network database models
With relational databases, it is
easier:
• For users to understand and implement a physical database system
• To convert from OTHER DATABASE STRUCTURES
• To implement projection and join operations (i.e., reference groups of related data elements not stored together)
• To create new relations for applications
• To implement ACCESS CONTROLS over sensitive data
• To modify the database
key feature of relational databases is the use of normalization rules to minimize the amount of information needed in tables to satisfy the users’ structured and unstructured queries to the database.
normalization rules include:
• A given instance of a data object has only one value for each attribute.
• Attributes represent elementary data items; they should contain no internal structure.
• Each tuple (record) consists of a primary key that identifies some entity, together with a set of zero or more mutually independent attribute values that describes the entity in some way (fully dependent on primary key).
• Any foreign key should have a null value or should have an existing value linking to other tables; this is known as referential integrity.
Object-oriented Database Management System (OODBMS)
means that all of the features related to object-oriented programming can be applied, including encapsulation (i.e., the creation of data types or classes, including objects) and inheritance (i.e., classes inherit features from other classes).
objects that contain both executable code and data
actual storage of the object in the database is achieved by assigning each object a UNIQUE IDENTIFIER
found a niche in areas such as engineering, science and spatial databases, and is often used when the database is made up of graphics, diagrams or sound that cannot easily be defined or queried by relational databases.