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The Master ChannelIntroduction
Introduction
- Cant create second twitter account ...
- Data modelling :build visual representation of the things that are relevant to a business and
their relationship between those things
Introductory example
- Starting a restaurant
- Process view : task: verbs → process modeling language
- Things (= entity type) we want to trace (not the same than process), that are stored in the
applications: an abstract representation of things that are relevant in the business: nouns →
context
o Can be shown by rectangles & a label that refers to the thing
1. Relationships (=business rules) : connection between things
o Verbs that describe relation
o Adding a line between entity types & verb
o Works in both ways
o Cardinality
▪ Zegt iets over de hoeveelheid van de ene tabel ten opzichte van de andere.
Er zijn 3 vormen:
▪ 1 op 1 ; one on one
▪ 1 op veel ; one on multiple *
▪ Veel op veel ; multiple on multiple
o Is the other side of the relationship mandatory or optional : the optionality of the
relationship
▪ 1 mandatory & 0 optional
2. Attributes: are individual data items that describe
something about the thing
o Connected to one entity type only
Different levels of data models
1. The conceptual : to understand the business concepts and how they are related
2. The logical : to see the details of the underlying entity types, attributes and relationships
3. Physical
- More specified if we go the right
,Logical : normalized
Translation to tables
- ERD = entity relationship diagram (= the implementation independent diagram) to table
format
o Create model of reality
- Translated to a xml document
- Entity types → tables & attributes → columns & real data → rows
-
- Special attributes : as they can be used to uniquely identify the rows in the table → = keys
- Primary keys in logical & physical data model
, - some thing can be filled in before
Modul test
,
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