Though I am super familiar with databases, the differentiation between a database, a database management system, and a database system is new to me.
Database = data and their supporting data structures; an organized collection of data; not generally portable across different DBMS
Database Management System (DBMS) = software package w/computer programs that control the creation, maintenance, and use of a database.
Database System = database data collection + DBMS; “implies that the data is managed to some level of quality.”
“In software engineering, an entity-relationship model (ER) is an abstract and conceptual representation of data.”
- A way to model databases
- Doesn’t show single entities or instances of relations, but sets.
I found the pictures very helpful in conceptualizing the structure of a database, and the relationships between data.
Entities = nouns
- Every entity must have “a minimal set of uniquely identifying attributes, which is called the entity’s primary key.”
Relationships = verbs
1. No repeating elements or groups of elements
2. No partial dependencies on a concatenated key
3. No dependencies on non-key attributes
The invoice>spreadsheet vs. database example is really clear, and helped me understand the “normalization process.”
Tuple = database row
NF1 addresses:
1. That a row of data can’t contain repeating groups of similar data
2. And that each row of data must have a primary key
NF2 addresses the fact that there can be no partial dependencies on a concatenated key
2 different table columns treated as a single thing = concatenated
NF3 addresses that there can be no dependencies on non-key attributes
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