Databases and SQL: Basic Terms

Databases and SQL

• Databases and SQL are part of week 1, day 1.

Agenda

• The agenda includes topics about basic terms and the Entity-Relationship Model/Diagram.

Basic Terms

• Data refers to the information.
• Database/databasesystem is a collection of data.
• Entity and entity Type is the object.
• Attribute is a property.
• A record is a data record.
• Relationship is a relation.

Data

• Data is a term used to describe a date in colloquial language.
• The term is broader in technical language and means information.
• Data of very different types can be addressed: Number, text, audio file or graphic/video file.

Database / Database System

• A database is generally understood to be a collection of data.
• There are 3 further requirements for databases from an IT point of view: New data added, data corrected/deleted, and data queried.
• The term "database system" can be used instead of "database" to clarify within IT.
• Both terms are synonymous.

Entity/Entity Type

• Data is used to address information that describes something
• This "something" can be a person, an object, an event, etc.
• Instead of a "something", the term "entity" will be used
• A database usually contains data for several entities.
• Each individual, specific person (and each individual car) represents an independent entity.
• However, all people have in common that they can be counted as the same entity type "person".

Attribute

• Data in a database describes properties of entities.
• Instead of "properties" the term "attributes" will be used in the future
• Several entities that belong to the same entity type are also described by the same attributes.
• These attributes assigned to the common entity types do not need to be repeated for each entity.

Data Set

• An entity type usually has several attributes assigned
• This means that several data are required to describe a specific entity
• A group of pieces of data belong together as they describe the same entity; this is called record in technical language.

Relationship

• Different entity types (or their entities) can be related to each other.
• The term "relation" can also be used for "relationship" in this case.

ERM

• ERM is the entity relationship model.
• ERD is an entity relationship diagram.

ERM/ERD Definition

• An entity-relationship model is a conceptual summary of all elements that are important for building a planned database.
• An entity-relationship diagram is the graphic representation of these elements.
• The diagrams consist essentially of showing entity types and relations.
• ER diagrams can be considered as a rough blueprint of a blank database.
• ER diagrams can be noted in different ways, the Chen notation will be used.

ERM/ERD Motivation

• Databases can be clearly presented with the help of ER diagrams.
• Peter Chen presented an initial example of graphical software development with his notation of the same name.
• This modelling or their diagrams are also used as the first step in a database design process.

ERM/ERD Short Excursion to the Database Design Process

• When commissioned to develop a database, the client usually has only an unspecific idea of ​​the structure of the desired database.
• The development of a database should therefore be divided into the following 3 sub-steps: Conceptual database design, logical database design, and physical database design.

ERD Symbols -> Entity Types

• Entity Types are displayed in a rectangle, for example person or auto (car).

ERD Symbols -> Attributes

• Attributes are displayed as oval.

ERD Symbols -> Composite Attributes

• A composite attribute consists of multiple other attributes.

ERD Symbols -> Derived Attributes

• Derived attributes are derived from constant sizes.

EDD Symbols -> Composite or derived Attributes

• During the conceptual database design these two aspects may be disregarded because it is only to determine all elements of the database structure requested by the client.

ERD Symbols -> Relation

• Relationships between Entities are displayed as a diamond.

END Symbols -> ID

• Always assign an ID attribute to each entity type identified by an underscore.