Class 2 | Week 2 | DAT601

Beginning this weeks second class Todd has provided an example document for our milestone one and is walking through it to help us understand the different types of tables he desires. Upon learning that this milestone is about 15 pages max I am feeling comfortable.

After this he has continued with last weeks power point and explaining more conceptual database concepts in depth, including but not limited to: cardinality, weak vs strong entities, multiplicity constraints and so on.


Below is some pictures from my teams brainstorming over our teams conceptual design done earlier today, nothing perfect but getting together to do this ignited some interesting conversation and I felt like we made progress in the end.


Below are my class notes for today
Cardinality

    cardinality is the count of entities within the relationship

Participation
    specifies minimum number of relationship instances each entity can participate in
    this is called minimum cardinality constraint
    two type of the participation are: Total and Partial


Double lines means the entity must participate in the relationship, single line determines that the relationship is optional

cardinality + optionality = multiplicity 
    
Attributes of relationships
    ex: for a WORKS ON relationship an attribute for this could be hours, how many hours did/does the      employee work on the project


Weak entity vs strong entity 

entity type that doesn't have a key attribute on its own is called a weak entity and the regular entity types that have key value is called strong entities

entities that fully depend on other entities to exist are weak entities, ex order details to order, order detail doesn't exist without an order in the first place.

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