380%20Sum11%20Cl60 - 380 Class 6 Data Modeling Click to...

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Click to edit Master subtitle style 380 – Class 6 Data Modeling
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Agenda o Modeling n Entities, Relationships - Cardinalities that reflect business rules
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Remember…how do you design databases? o We’ve been doing the bottom up approach - n Bottom Up approach – Normalization o Take existing data fields and store them in most efficient way possible o Now we’re going to be looking at the top down approach - n Top Down approach via Data Modeling o Develop a database based on Logic/theory, then translate into a physical database
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Data Modeling Constructs o Entities ( Tables ) n Sets of real world objects – things that have a separate existence, either physical or conceptual o Think about Sets of Instances (i.e., many Customers) o Relationships ( Foreign key(s) and Tables ) n Associations between entities n Relationship doesn’t exist without the entities that create it
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Example Entities and Relationship Student Course Draw as:
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Entities have Attributes i.e. tables have fields/columns o Attributes (fields) n The data that is useful for business decisions n Simple versus composite attributes o ‘Simple’ is as uncomplicated as it can get. (SSN) o Composite – can be further decomposed (Address breaks down into Street address, City, State, Zip) n Derivable attributes o Static – will not change if new data is entered into system (Might store these e.g. invoice total) o Volatile – will change if new data is entered into system (Calculate these, e.g. . GPA, inventory on-hand)
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Types of Entities/Relationships o Entities n Resources (nouns) n Economic Events (verbs) n Agents (internal and external) (names) + Types of each of the above (next class) o Relationships n Stockflow (relationships between resources and events – increase or decrease) n Duality (relationships between increment and decrement economic events) n Control (relationships between events and the agents that participate in them)
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Describing Entities’ Relationships o Participation Cardinalities (Min,Max) n Minimum cardinality : (i.e., Does each Sale require a customer? ) 0 = optional participation 1 = mandatory participation n Maximum cardinality : (i.e., Each Sale can have how many customers?) 1 = one-time only participation N = as many times as needed, no restrictions (Min,Max) Sale Customer
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380%20Sum11%20Cl60 - 380 Class 6 Data Modeling Click to...

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