Chapter 5

Databases

Right, so we have developed for ourselves a good understanding of what the computer side of MIS looks like.  I think with a stronger understanding of that component we can get a start on the software side.  Databases are a core component of many MIS systems and are in general especially valuable to modern business models when they have been developed and implemented properly. Right, so what is a database?  The definition is a self-describing collection of integrated records.  Databases are comprised of tables which can be thought of as a what you might put on a single Excel sheet if it only contained on group of information.  Tables are made up of Fields which would be the columns and Records which would be the rows.  Knowing that makes the definition of databases a little more clear.  It is a collection of integrated "rows".

The Parts

Okay so we have tables, fields and records down but there is quite a bit more to it than that.  Each table will have a Key or a field that makes each record unique.  This will allow us to diffeentiate between records when one table develops a relation ship with another.  It is important to ensure that the each record has a unique key for those relationships to function, using names or vehicle models is often not the way to go as it is likely different records will have the same name or model and it may not even be the same entity we want to refer to.  The key or "Primary Key" will continue to be important as will the "Foreign Key" which is simply an entry in one table that is the key in another.  This is how we develop those relationships from one table to another.  This occurs in the relational database which is a group of tables in our full database that tracks and controls the relationship of of foreign keys.  This is where metadata becomes a thing.  Metadata is data that describes other data.

Database Management Systems

Database management systems are simply programs that are used to create, process and administer databases.  There are many different ones out there and most are horizontal applications that can be used across a wide array of industries for a wide array of purposes.  Managing data in the modern business world is almost a universal demand.  However, there are more vertical applications that are databases such as SAP specializes as a company in producing business management database software and programs such as QuickBooks Pro are actually databases with very specialized designs.  We are going to continue to think of or programs as highly customizable databases however as it allows us to glean a broader understanding of what they are.  So first the DMSs can create a database, a manger can create custom fields and records in custom tables.  They can the designate how those tables relate to each other by the use of the table's keys in other tables.  This sounds complicated but the image below should help in understanding it.

 In this example the key for the Students table is ID# while the key for Courses is Class ID.  In the Takes_Course table ID# and Class ID are foreign keys allowing us to create a relationship between students and the classes they are taking.  The DMSs also process data by  allowing users to read data, add data, modify existing data and delete existing data withing the already existing tables.  Users can also add structure to the database by adding fields or tables to increase the functions of an existing database.  This process is often very labor intensive so it is important to ensure the database is well designed from the get go.  

Another thing to know is that these programs can exist in both web based applications as well as traditional applications.  The differences between the two exist as we previously discussed how ever there is a caveat to web bases applications that is more significant when talking about databases.  Databases contain large amounts of data as their inherent purpose to make large amounts of data manageable and usable.  That data is often very valuable and keeping away from prying eyes is often very important is it can cost companies lots of many when their databases are compromised.  Web based databases are more vulnerable to exterior security threats and therefore have a greater risk of being comprised and a greater cost to keep secure.

Designing Databases

Models are used intially to create a way to easily visualize the relationship tables and entries will have with each other and how the keys to each table will be used.  The most common way to do this is using the Entry-Relationship Data Model which is essentially a web chart specialized for use in a database.  Entries or things users want to track can be designed to have specific type of relationships with other tables.  An entry can be required to relate to only one entry on the other table, called one to one or it can be allowed or required to relate to many other entries in the other table, called one to many.  As long as we maintain unique keys in each table this remains possible.  The dictation of these relationships are controlled using cardinalities which can be maximum or minimum meaning the relationship must have x number or carinalities with another table.  The x is determined while designing the table.  It is possible for x to be zero meaning that a relationship is not required between the two entities.

Below is an example of an Entry-Relationship diagram which shows the relationship of tables in a database.  You can use the key in the image to understand what the notations on each relationship line means and how it dictates those tables interact with each other.