Databases and Structured Files: What is a database? A database is a collection of information Databases are typically stored as computer files A structured file is similar to a card file or Rolodex because it uses a uniform format to store data for each person or thing in the file 12/4/2018 CIS270

Fields: What is the basic element of a structured file? A field contains the smallest unit of meaningful information, so you might call it the basic building block for a structured database Each field has a unique field name that describes its contents A field can be either variable length or fixed length. 12/4/2018 CIS270

Who defines the structure for the records in a file? The person who creates a data file defines the fields it contains Each kind of record is referred to as a record type A record type is similar to a blank form, and it is usually shown without any data in the fields A record that contains data is referred to as a record occurrence, or simply “a record.” 12/4/2018 CIS270

What are relationships? In database jargon, a relationship is an association between data that’s stored in different record types One important aspect of the relationship between record types is cardinality Cardinality refers to the number of associations that can exist between two record types A particular order cannot be placed jointly by two customers When one record is related to many records, the relationship is referred to as a one-to-many relationship 12/4/2018 CIS270

What are relationships? A many-to-many relationship means that one record in a particular record type can be related to many records in another record type, and vice versa A one-to-one relationship means that a record in one record type is related to only one record in another record type Relationships between record types can be graphically depicted using diagramming techniques, such as an entity-relationship diagram, sometimes called an “ER diagram” or “ERD.” 12/4/2018 CIS270

Hierarchical, Network, Relational, and Object-Oriented Databases Several database models exist Some models work with all of the relationships described earlier in this section, whereas other models work with only a subset of the relationships The four main types of database models in use today are hierarchical, network, relational, and object oriented 12/4/2018 CIS270

What’s the simplest database model? The simplest database model arranges record types as hierarchy In a hierarchical database, a record type is referred to as a node or “segment.” The top node of the hierarchy is referred to as the root node A parent node can have more than one child node A child node can have only one parent node 12/4/2018 CIS270

What’s a relational database? It produces databases that are difficult to create, manipulate, and maintain A relational database stores data in a collection of related tables Each table (also called a “relation”) is a sequence, or list, of records. All of the records in a table are of the same record type 12/4/2018 CIS270

What’s a relational database? A row of the table is called a tuple, and is equivalent to a record The columns in the table are called attributes, and are equivalent to fields In a relational database, relationships are specified through the use of common data stored in the fields of records in different tables 12/4/2018 CIS270