Conceptual Modeling by oogACE

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									Conceptual Modeling




                  Database Principles
What is a Conceptual Model?

• A mental model of the world around us
• Models necessarily mean simplification/abstraction



         Possible Conceptual Models
          1: Autumn in the Gunks

          2: F = GMm/R2




                                   Database Principles
Exercise: Imagine a Conceptual Model

• Working in groups of three or four come up with various
  conceptual models for one of the following (make sure
  everyone contributes):




     Hallowe’en
                                Christmas            First Day at School




                             Buying a Cow


                            Database Principles
Things we see in your examples:

•   Models often reflect modeler’s point of view
•   Some models are quite specific – single detail
•   Some models are quite general/abstract
•   Modeling language can differ – natural, picture, song
•   Hard if you are not familiar with the situation
•   Not everyone in the group contributes the same
•   Did someone lead the discussion?
     – Organizer vs Idea person




                         Database Principles
Hotel Example:

             Model a Hotel and its Operations.
• Divide yourselves in groups again
• Each group pick on of the following areas:
   – Reception (mine)
   – Kitchen
   – Room Service
   – Reservations
   – Concierge
   – Restaurant




                       Database Principles
Database Principles
Observations:

• New, graphical language
• Lots of detail hidden or missing (how many messages?)
• Diagrams overlap in some places
• Each diagram shows only part of the big picture
• Synonyms? Homonyms?
• Not all information is modeled
• What happens if one department “owns” its own data?
   – Is it always possible?
• Leader? Negotiation? Different points of view ok?
• Our diagrams show areas of responsibility, a business
  model even!!

                      Database Principles
Summary:

• Our individual views are called external views.
• If we were to combine them in a single picture,
  negotiating synonyms and homonyms, we would have a
  conceptual model of a hotel business.
• This conceptual model would be a first step towards a
  design for a database for a hotel but it is a picture of
  reality, not a database.
• Graphical languages let us see everything at once
  instead of sequentially as text does.
• Our language needs to be more expessive
• People can be productive in teams if they have a
  common goal and good tools.

                       Database Principles
Formal Definitions:

• A conceptual schema/model is a map of concepts and
  their relationships.
• An external schema/view represents one person’s view
  of the world around her.
• In the context of database, a conceptual model is the
  merging of various related external views.




                      Database Principles
Homework (on the web):

• Read the poem “The Blind Men and the Elephant” and ...




                      Database Principles
                         The Blind Men and the Elephant

Six wise men from India,                               The fourth had come upon the trunk
An elephant did find.                                  Which he did seize and shake,
They set about to feel its parts,                      Quoth he, "This so-called elephant
(For all of them were blind.)                          Is really just a snake."

The first he felt towards the tusk,                    The fifth had felt the creature's ear
"It does to me appear,                                 And fingers o're it ran,
This marvel of an elephant                             "I have the answer, never fear,
Is very like a spear."                                 The creature's like a fan."

The second sensed the creature's side                  The sixth had come upon the tail
Extended flat and tall,                                As blindly he did grope,
"Ahah!", he cried and did conclude,                    "Let my conviction now prevail,
"This animal's a wall."                                This creature's like a rope."

                                                       And so these men of missing sight
The third had reached towards a leg
                                                       Each argued loud and long,
And said, "It's clear to me,
                                                       Though each was partly in the right
What we should all have said instead.
                                                       They all were in the wrong.
This Creature's like tree."




                                      Database Principles
Homework (continued):

• Prepare a conceptual model of an elephant, using as
  your starting point, the external views expressed by each
  of the men in the poem.
• Find out what you can about the poem and its author.
• Explain how the poem relates to the task of creating a
  conceptual model of an organization’s information.
• The poem does not introduce a “seeing” man who can
  set the blind men straight. Who plays the role of the
  seeing man in the organizational context?




                       Database Principles
Homework (continued):


• One student once gave me the following answer:

                 A fan, a spear, a wall, a rope,
                 A snake up in a tree,
                 Disparate views,
                 We can not hope,
                 Will represent reality.



Why is his skepticism unlikely to be a problem in in creating
 a conceptual model of an organization’s information.




                             Database Principles

								
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