Database Design for Mere Mortals
Summary of Chapter Six & Seven in Database Design for Mere Mortals
Chapter six begins discussion on the importance of analyzing an organization’s current database. Author Michael Hernandez states that in order to know where you should go, it’s necessary to understand where you are. What he means is the current database being use is a dependable resource for developing a new database. The database developer needs to answer three questions;
1. What types of data does the company or organization use?
2. How does the company or organization manage and maintain that data?
3. How does it use that data?
The answers to these questions create guidelines for the new database structure. Now you can design a database that best suits the organization’s needs. Next step is reviewing the various ways data is collected; paper based database (index cards, hand written reports, and preprinted forms), legacy database (database in existence and in use for five years or more), or just the memory of some of the employees. The three steps used in the analysis process; review the way data is collected, review the way information is presented, and conduct interviews with users and managers.
Conducting interviews are useful in the analysis phase .
• They provide details about the samples you assembled in reviewing how data is collected and how information is presented
• They provide information on the way the organization uses its data
• They are instrumental in defining preliminary field and table structures.
• They help to define future information requirements.
The conducting interview process as two parts: the first part involves interviewing the user, then interviewing the management. During the interview, the developer will have the opportunity to use both open ended and closed questions. Use open ended questions focus on specific subject (“How would you define the work that you do on a daily basis?”) and closed questions to obtain specific details on a particular subject (“Do you enter data into the database?”(Yes/no answer)). The next discussion talks about two techniques that are crucial to the success of interview process: the subject identification technique and the characteristic identification technique. Subject identifier helps you identify subjects that need to be addressed by the database. Characteristic identification technique is the appropriate nouns identified on your list. This becomes your list of characteristics. According the Michael Hernandez, Conducting user interviews are the sum of four issues:
• The types of data users are currently using;
• How users are currently using their data;
• The data collection samples, report samples, on screen presentation samples you assembled during the first two steps of the analysis;
• The types of information users need in conjunction with their daily work.
This section follows up with a discussion about conducting management interviews. I believe it is very important to ask the management personnel about the three requirements:
1. Additional information requirements; determine whether they require some supplemental information that is currently missing from your report.
2. Future information requirements; ask management what information they foresee needing in the future.
3. Over all information requirements; determine whether there is any data that the organization needs to maintain that has not been discuss before.
Finally the author examines the process of compiling a list of fields based on list of characteristics and any characteristics that appear in sample reports (pg34). List fields are broken into two parts. Preliminary field list; is the data requirement of the organization core field set that will be define in database. Calculated field list; stores the result of a mathematical calculation as its value. Calculated fields are creating separately to be use later for calculation purposes.
Chapter seven opened with the discussion of the preliminary table list from the previous chapter. The database developer will use three procedures to develop a preliminary table. One involves using the preliminary field list; two using the list of subjects collected the user and managers interview forum, three using the mission objectives defined at the beginning of the database design process. When the preliminary table list is complete, transform it into a final table list. Next add two elements on the preliminary table list: table type and table description. Table type are use to identify tables with similar functioning characteristic.
There are four table types:
• Data. This table type stores information data and represent important subject to the organization.
• Linking. This table type is used to establish links between two tables in a many to many relationship.
• Subset. This table type contains supplemental fields related to a particular data table.
• Validation. This table type
Table description is used to give a clear definition of the subject represent by the table and to state why the subject is important to the organization (pg9). The author Michael Hernandez conveys a set of guidelines for creating table names. These guidelines ensure names are clear and unambiguous, descriptive, and meaningful, and descriptive name that is meaningful to the entire organization. Enlist the help of users and management to establish good table description for each table. Conduct interview with both groups at the same time to get a consensus regarding the description of each table. Collect notes and compose the descriptions, then confer with both parties once more to make certain that the descriptions are acceptable and simple to understand by everybody.
Assigning fields to a table is a simple process: figure out which fields represent characteristics of the table’s subject and assign them to that table. Repeat this process for all tables on the final table list. If you feel that fields or set of fields can represent characteristics of more than one table, then assign them accordingly.
Next subject of discussion is refining the field; you refine a field by improving the field names and fixing any issue existing between them. The guidelines for creating fields are the same as in the previous chapter. The best way for a developer to identify potentially troublesome fields is to learn the elements of the ideal fields.
Once you learn the elements of the ideal, you will be able to identify poorly design fields easily. Author Michael Hernandez discussed the procedures for resolving multipart fields and multi valued fields. Multipart fields are difficult to work with because they contain more than one item of data. In order to resolve a multipart field, you need to identify the separate items making up the field and treat each one as an individual field.
Multi valued field bring about the same degree of difficulty as multipart fields. A multi valued field represents two or more occurrences of the exact value. This causes problem when you try to enter more occurrences of the value than the field will allow. The only solution have is to make the field larger every time you need to enter more values than it will currently allow.
Chapter seven closed with a detail discussion on the process of refining table structure. We also learn to identify the elements of the ideal field.
Next to resolve unnecessary duplicate fields, you purge the database of any unnecessary fields then refine the tables to be in accordance with the ideal table.
In conclusion, author Michael Hernandez discuss the topic of subset tables. A subset table is a table connected to some particular table in the database. Each subset table contains only those fields that describe a specific version of the subject represented by the main table. A field from the main table is included in order to connect the main table together with the subset table (pg29).
Work Cited
Hernandez, Michael J. (2003). Database Design fore Mere Mortals, Second Edition. Boston, MA: Addison-Wesley