Databases

Databases

1. Organized collection of data

   • Relational Database
     • Information stored in different tables that relate to each other
       • Tables consist of rows and columns (similar to a spreadsheet) where each column represents one piece of information about the customer and each row represents a collection of information for that specific customer
     • Data stored in a series of tables . In a business , the tables are related according to the Business rules of the organization.
     • Things to consider when designing a relational database:
       • How many tables are required to store data in the database?
       • Which columns (or pieces of information) belong in each database?
       • How do the databases relate to one another? , that is to say what are the business rules?

2. Help work with large amounts of data

3. Problems storing data in other ways than a Database

   • Size: As size increases, it can take a longer period of time to open the document
   • Ease of Updating: Unlike Excel sheets, Databases can be used at the same time by many users and processes
   • Accuracy: In excel sheets, its easy to input an invalid prompt vs Databases have strict parameters that force users to put in a valid value
   • Security: Unlike Excel documents where either everyone can view a document, Databases can insure that only authorized individuals are able to see sensitive information where as everyone else has a customized "view" of the database that they see.
   • Redundancy: Unlike Excel documents, Databases can be set to automatically create the same piece of data in two or more different places. That means that when the original Master database is updated, all others will also be updated , and if it goes down then we have not lost all of our data. The problem arises when excessive or wasteful amounts of data is stored.
   • Importance: Data is important and so having it stored in a secure environment where the authorized individuals have access is more crucial than having a spreadsheet that is viewable by unauthorized individuals

4. Are mantained with a Database management System (DBMS)

   • Examoles include: SQL Server, Oracle, Access, MySQL
   • Databases are Data and Rules where as the DBMS is the way we interact with our databases
   • DBMS
     • Data Defination Language (DDL): facilitates the creation and manipulation of meta data. Helps define the structure of the database
       • Examles include Column Definations, Constraints on data
     • Data Manipulation Language (DML): Helps with the creation and the manipulation of the data stored in the database
       • Examples: Records
     • Data Control Language (DCL): ensures the security of the data. Allows access to the data in the database to authorized users only
     • Query Language (QL): Acts to retrieve data from the database
     • Proprietary Language and Tools is a programming language used by developers to create programs that make up the system.
     • Database Engine:Core set of programs that make up a DBMS. Are executed when a request is sent to the DBMS. For example the Application Program created by the developers would issue a Data Manipulation Language (DML) statement to the DBMS which would then interact with the Database.
       • Note: Developers or users (Stakeholders) DO NOT INTERACT DIRECTLY WITH THE DATABASE!

5. Creating a Database

   • First step: Review Source documents and talk to the end users to identify
     • Data items that must be stored
     • Business rules the application must adhere to enforce
       • For example, for an application that manages the issuing of driver’s licenses, an applicant must be sixteen years of age in order to acquire a driver’s license. A good database design will account for the business rules enabling the DBMS software to enforce many of these rules.
   • Second step: Create a Logical Database Design
     • Represents users and programmers perception of data stored in the database.
       • I.e How it would look like in a table
     • Entity Relationship Model (Data Model) and Normalization process are tools used to complete the logical design. Describes the business scnerio in terms of entities and relationships.
       • Entities: represent a thing that exists in the word. For example a Customer or a Course or a Item
       • Relationship:Represents a dependency between entities based on the Business rules of the organization
         • Example: The following business rule may apply: many customers can place orders for merchandise but a specific order is placed by one customer. This results in a one-to-many relationship between the customer entity and the order entity.
       • When using a relational database management system each entity becomes a table in the database.
       • Normalization is a set of guidelines for creating the logical design for a relational database. Normalization helps database designers decide: • The number of entities/tables required within the database. • Which attributes/columns belong in which entities/tables.
     • Depicted graphically as an entity relationship diagram (ERD)
       • The IDEF1X notation is used for all ERDs in this course. IDEF1X was adopted as a standard for data modeling by the National Institute of Standards and Technology (NIST) in 1993.
   • Third step: Physical Design
     • Describes the physical implementation of the logical design

6. Iterative process which changes depending on when requirements or information is discovered

   • During this process a "view " is created. A view is the data used to complete one task within the application. For example Add a customer.

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