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Intro

File-Processing Systems limitations: lack of: integrity, standards,

flexibility/maintainability

The above stems from two main problems: lack of data integration,

lack of program-data independence

Definitions

External schema - different user views or subschemas whichdescribe portions of the database of interest

oViews - information of interest to a particular user group (e.g. a view of the myUH db shows class name, dates, teacher

and rm #) Internal schema - describes the physical structure of the stored

data (technology dependent)

Data independence - means the view and the physical data arenot dependent

oPhysical data indep - e.g. the DBA can move info to differenttables without the user ever noticing a difference

oLogical data indep - e.g. one user view doesnt affect anotheruser view

DBMS - database mgmt system, software that facilitates themanipulation of a database

Database system - self-describing collection of interrelated data;includes data and metadata

Distributed database (DDB) - multiple logically interrelateddatabases that may be geographically dispersed

Distributed database mgmt system (DDBMS) - used to manageDDBs (user is not aware of data's geo location)

Data warehouse - repository for data so it can be used bydecision makers

Data definition language (DDL) - Used for creating db structureslike tables and views; typically SQL

Data control languages (DCL) - handle administrative tasks likebackups and security, typically SQL

Data manipulation languages (DML) - facilitate modification ofactual data; typically SQL

Data dictionary - stores information about data (metadata) suchas relationships, authorizations and usage

Data repository - metadata about data models and applicationprogram interfaces Data model - used to represent real world phenomena, the

blueprint for db design

Universe of interest - myUH has info about students, classes,teachers, financial aid, etc. 'Types of insects' is probably outside

myUH's universe of interest

Requirements specification - interview users and review businessdocuments to understand rules and objectives

Business rules - organized set of restrictions describing theorganization's activities

Semantic modeling - the first step in db design, rules set forth bythe business

Conceptual modeling - the second step in db design, refers onlyto data specs, not business processes

Data types - numeric, alphabetic, alphanumeric Derived attribute - e.g. instead of storing birthday, it is calculated

by subtracting DOB from today's date

Integrity constraints - rules that govern the behavior of data atall times in a db

oDomain constraint - ensures the value is valid, e.g. 'StudentID'can only store numbers, not letters

oUniqueness/key constraint - requires instances of an entity tobe unique when compared to other instances

Key attribute - one or more attributes that make an instanceunique

Non-key attribute - e.g. Since many students have a 'garage passit does not help you identify a specific student instance

Attributes - underline the primary key/unique attribute. Use adarkened circle for mandatory attributes, outlined circles for

optional attributes, double circle for multivalued attributes

Cardinality - the maximum amount of participants in arelationship. e.g. look for wording like a teacher may have up to

55 students. This is max in (min:max) notation.

Participation constraint the minimum participants in arelationship. Look for may(0 or optional) or must(1 or as many

as are specified). This is min in (min:max) notation.

Domain constraint - indicates what type of values is acceptable,such as only dates or only numeric. Also indicates the amount of

characters that are accepted [A,4] means alphanumeric and 4

characters.

Deletion constraint:ocascade -> if you delete a parent all the children get deleted, C

near child;

orestrict -> don't allow you to delete parent if children exist, Rnear parent;

oset default -> change a child's parent to some other parent toallow delete, D near child;

oset null -> delete parent and allow child to have no parent, Nnear child

Comparisons

Entity type vs. instance - Student is an entity type. A specificstudent, like Joe Stood, is an instance. Instance is sometimes

referred to simply as an entity

Base(strong) vs. weak - Base entities are those that haveindependent, unique instances. Weak entities depend on

their parent entity for uniqueness.

Parent vs. child - look at the participation. A child must havea parent but a parent may not have a child

ERD: Presentation vs. coarse vs. fine - presentation is themost basic and fine is the most detailed

Diagraming

1. Identify the 'business rules' within the providedinformation/paragraph. Treat this is a checklist and crossitems off when complete. Look for:

a.Entity typesb.Unique and non-unique attributes for each entity typec.Relationships between two or more entity typesd.Participation between entity types, may means optional

participation, must means full participation

e.Cardinality between relationship types meansf. Specific wording like:

1.May, must, might, may or may not, plural nouns vs.singular nouns (words that end in s vs words that

begin with a or an)

2. Draw the diagram3. Write a bulleted list of 'business rules' that were unable to be

expressed in the diagram. This might include specificmin/max values, domain constraints, relationship arcs, etc.

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NOTE: These diagrams do not have primary key underlined because

its too difficult to do in DiaPortable

Presentation Layer ER Diagram

1.List all entities inside a square, use a noun2.Write the relationship between the entities, use a verba)Draw a vertical line if biz rule says participation is a mustor

draw an open circle if biz rule says may. Dont forget look

across.

b)Write a 1, n, or m to indicate the maximum (cardinality)3.List all attributes for each entity, underline the unique

attribute(s), use a double circle for multi-valued attributes, use

an open circle for optional attributes. Use a dotted underline for

the partial key in a weak attribute

4.Write any remaining Semantic Integrity Constrains which arethe remaining biz rules that cant be described by a simple

Presentation Layer ERD

Coarse Granular ERD

1.Follow all the steps from the previous diagram but make themodifications listed in the next step

2.Convert your lines and circles from steps 2a and 2b to (min:max)notation. Circles become 0 in front of the colon. Vertical lines

become 1 in front of the colon.

3.Add deletion constraints.

Fine Granular ERD

1.Follow all the steps in the previous diagram. e.g. (min:max),deletion constraints, etc.

2.Add domain constraints. e.g. [X,9] for 9 alphanumeric characters3.Separate M:N relationships using a weak entity in the middle.4.Break multi-valued attributes into weak entities.

Above is a Coarse Granular ERD. Below is what results after you

convert it to a Fine Granular ERD