preps | erm | entities | relationships | | sql
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What are the components of a relational database and
how do they compare with what we already know?
a database is a collection of related data
a database management system (or DBMS) is a system designed for two main purposes
a flat file database is one where all the data is contained in a single table, such as in Excel
a relational database is one in which you can store information in different tables, each containing different information that relates to information in the other tables
an entity-relationship model (ERM) is an abstract and conceptual representation of data. Entity-relationship modeling is a database modeling method, used to produce a type of conceptual schema or semantic data model of a system, often a relational database, and its requirements in a top-down fashion. Diagrams created by this process are called entity-relationship diagrams (or ER diagrams)
One has choices in how to model the elements in a database. One of the standard textbooks on the topic (Elmasri, R., & Navathe, S. (2011). Fundamentals of database systems. Boston: Addison-Wesley.) offers a view of the several methods.
The purpose of a database is to store information about certain types of objects.
[let's use this example to discuss the topic]
To make the distinctions clear, we will use a color schema in which we use
terms relevant to entity relationship models
and their correlates in Excel
ERModel entity set | Excel worksheet |
composed of entities | composed of rows |
which have attributes | which have column cells |
type | ⇓⇓⇓⇓⇓⇓ | |
ERModel entity set | composed of entities | which have attributes |
Excel worksheets | composed of rows | which have column cells |
[like books] is an abstract definition of something
in Excel, there is no correlate as it is just a definition, not an example of a definition
is the list of given entities/rows within a given entity class that are currently in the database/worksheet
in Excel, an entity set is a worksheet
[like a textbook for INLS161] is a concrete example of that description
in Excel, an entity is a row
attributes/columns include information we want in the database
attributes/columns help to uniquely identify individual entities within a class
attributes/columns can describe relationships between entities in different classes
in Excel, attributes are columns
is a set of attributes/columns that uniquely identifies an entity/a row
is a copy of the Primary Key
of one entity/row
that appears as
an attribute/column
in another entity class/worksheet
and helps define the relationship between
entities/rows
in the two entity classes/worksheets
16 April lecture | preps | erm | entities | relationships | sql