Data Notes
Good luck to all of you 🙂. Also I made these notes over night so there might be some issues…

Part I: Structured Data

Entities and Relationships

ER model - only a description. Graphical notation only. 

We start with a rectangle. Attributes go to circle.

  • Superkey = A set of attributes is a superkey for an entity if those attributes, taken together, always uniquely identify every entity instance. Might have attributes that are not needed for identification.
  • Key = A set of attributes is a key if it is a minimal set of identifying attributes — removing any one attribute would make it no longer uniquely identifying.
  • Super key  = for any instance always unique
  • Key = minimal set of identifying each entity
  • Candidate Key = we might have more options which keys to use - candidate represents this choice
  • Primary key = a candidate key we actually choose.
  • Key is a set of attributes. Key made of more than one attribute is called composite key.
  • We underline all the keys used to compose the primary key

More on keys here:


ER diagrams are just this bullshit. 

Relational Model

Some types of relationships:
  • Many to one
  • One to many
  • Many to many

Key constraint = if a relationship must occur only once. Arrowhead

Total participation:

This means that a student has to be member of lab team but does not need to be a leader. Basically its a not null for foreign key. We indicate this with double line.