Data, Information & Knowledge Database DBMS Types of Models E-R Model
Mar 26, 2015
Data, Information & Knowledge
Database
DBMS
Types of Models
E-R Model
Knowledge is what we know
helps us know where things are
It also contains our beliefs and expectations.
It is from this “map” that we base our decisions,
constantly updated
You can’t currently store knowledge in anything other than the brain
two sources that the brain uses to build this knowledge - information and data.
facts of the World
description of the World.
We can perceive this data with our senses, and then the brain can process this.
knowledge was limited by our direct experiences.
can capture data in information, to be accessed at different times.
The information can be lost, but the data can’t be.
Data is always correct (I can’t be 29 years old and 62 years old at the same time)
but information can be wrong (there could be two files on me, one saying I was born in 1981, and one saying I was born in 1948).
Information captures data at a single point. The data changes over time.
Mistake : information is always an accurate reflection of the data.
Collection of data ?
not every collection of data is a database
An organized collection of related data
Eg ?
Keep records of our: Clients Staff Volunteers
To keep a record of activities and interventions;
Keep sales records;
Develop reports;
Perform research
A software package/ system to facilitate the creation and maintenance of a computerized database.
A database's properties are determined by its supporting DBMS and vice-versa
Availability Efficient access Abstraction
• Protection or Security measures to prevent unauthorized access
• Reliable storage & recovery of 100s of GB• Querying/updating interface and API• Support for many concurrent users• Backup and recovery services.
DataData InformationInformation KnowledgeKnowledge ActionAction
Is to transformIs to transform
Navigationalpointers from one record to another. eg: hierarchical model, Network model
Relational modelsearch for data by content, rather than by following links
Entity-relationship modelto overcome the problems of Relational model as a modelling lang.
Object database and the XML database : for multimedia, engg, documents etc.
for representation of real-world
represents overall logical structure of information grouping of data elements inter-relationships between groups
simple and easy-to-use
permits top-down approach for controlling details
useful as a tool for communication between designer and user during requirements analysis and conceptual design
Entity
Entity set Strong entity type Weak entity type ( discriminator / partial key)
Attributes Simple and composite attributes Single valued and multi valued attributes Stored and derived attributes Null attribute Key attribute
Relationships Degree
Cardinality
Mapping cardinalities One to one One to many Many to one Many to many
Participation constraints Total participation Partial participation
Keys Super key Candidate key Primary key Foreign key
Why EER Modelling?
Inheritance
Specialization
Generalization
Emergence of new technologies
Semantic data modeling concepts
Employee Secretary Technician Engineer Manager Clerk
Sub class Super class Inheritance
Define a set of subclasses of an entity type
Establish additional specific attributes with each sub class
Establish additional specific relationship types between each subclass and entity types or other sub classes
The set of subclasses is based upon some distinguishing characteristics of the entities in the superclass
• May have several specializations of the same superclass ▪ {PERMANENT_EMPLOYEE, TEMPORARY_EMPLOYEE}
based on method of pay▪ {FACULTY, CLERK, TECHNICIAN}
based upon job type
• specific attributes▪ Eg : TypingSpeed of SECRETARY
• specific relationship types▪ Eg: HOURLY_EMPLOYEE can BELONG TO some TRADE UNIONs etc.
Inverse process of specialization
Identify the common features of several entity types
Generalize them into a single super class
Eg : Employee is a generalization of {SECRETARY, ENGINEER, TECHNICIAN}
Types of specialization
Constraints on specialization
Specialization & Generalization Hierarchies Lattices
Summary
Predicate defined
Condition specified
Conditions are specified on the values of some attributes in the superclass
Defining predicate
Eg: JobType = “Secretary”
Attribute defined If all subclasses in a specialization have membership condition on
same attribute of the superclass
Defining attribute
Eg: JobType
User Defined No condition for determining the membership of the subclass
Specified individually for each entity by the user
“Secretary”“Engineer”
“Technician”
Job Type Defining attribute
Defining predicate
Disjointness Constraint Subclasses of the specialization must be disjoint An entity can be a member of at most one of the subclasses of the
specialization Not disjoint Overlap
Notation
d ODisjointness Overlapping
A patient can either be outpatient or resident, but not both
A part may be both purchased and manufactured
Completeness Constraint Total
every entity in the superclass must be a member of some subclass in the specialization/ generalization
Shown in EER diagrams by a double line Eg: Employee {Hourly_Employee, Salaried_Employee}
Partial allows an entity not to belong to any of the subclasses Shown in EER diagrams by a single line Eg: Employee need not be {Secretary, Technician, Engineer}
A patient must be either an outpatient or a resident patient
A vehicle could be a car, a truck, or neither
Hierarchy: Every subclass has only one superclass single inheritance
Lattice: A subclass can be subclass of more than one superclass multiple inheritance
Same for generalization hierarchies or lattices
Shared subclass: A subclass with more than one superclass
In a lattice or hierarchy, a subclass inherits attributes not only of its direct superclass, but also of all its predecessor superclasses
Specialization top down approach
Generalization bottom up approach
In practice, the combination of two processes is employed
Binary or ternary relationships ?
Constraints on n-ary relationships
Aggregation
Union / Category
On the basis of semantics of the situation
SupplierProject
Part
Supply
SupplierProject
Part
Supplies
Can supply
Uses
Solution 1:
Include the ternary relationship + 1 or more of the binary relationships (if they rep. diff. meanings & if all are needed for the appln.)
Solution 2:
Represent the ternary relationship as weak entity type with NO partial key & identifying relationships.
1. Cardinality Ratio Notation
1, M, N
2. Min, Max Notation
ER Model can’t represent relationships among relationships
Aggregation : To represent relationship between a whole object & its
component parts
Relationships are treated as higher level entities
Chapter 4-51
CAR
Chassis (steel frame)
OtherSystems
Drive-train
represents IS-PART-OF (component) relationship
Root class: CARComponent Classes: Chassis, Drive-Train, Other Systems, WheelsRoot class: WheelsComponent Classes: Tires, Tubes, Hub-Caps
Wheels
Tires Hub-CapsTubes
Suppose we want to record managers for tasks performed by an employee at a branch
Engineering_Manager Engineer Manager Salaried Employee
Need to model a single superclass/subclass relationship with more than one superclass
subclass = collection of objects i.e. a subset of the “union” of distinct entity types
SHARED SUB CLASS
subset of the intersection of its superclasses
shared subclass member must exist in all of its superclasses
Attribute Inheritance : Total
CATEGORY
subset of the union of its superclasses
category member must exist in any of its superclasses
Attribute Inheritance : Selective
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