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Example research essay topic: Files Our Group Creating The Table Tables - 1,071 words

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As the database team, it was our job to provide a storage facility for the other teams. We had to come up with a design that was flexible enough to handle the various types of data and yet robust enough to make searching and record lookup efficient. Since Oracle is available in the lab and is a very powerful database management system, we decided to leverage our assets and create the database on perhaps the best database server available. But before we could slap together some SQL commands we had to plan some things out first. Schema The process of building our database consisted of many phases of analysis before the actual design. We had to create an outline, and distribute it to the groups for feedback.

Upon receiving the feedback and suggestions, we constructed the Entity-Relationship Diagram. Then we transformed the ERD into a prototype of the tables in the database and asked other team members for approval. Then we made final layouts of the tables, which consisted of the actual names of the tables and their corresponding attributes. These layouts were distributed to the other teams so that they can incorporate our design into their servlets. Constructing an ER diagram is very important because the ER diagram is most often used as a tool for communication between database designers and end users during the analysis phase of database development.

The process of designing the ERD consists of defining the types of entities: strong entities, weak entities, and the important attributes associate with each entity. Each entity has many attributes associated with it. Examples of data attributes for the customer table are customer id, customer name, etc. We composed the data into six entities: customer, order, books ordered, music ordered, books, music, and track list. The symbols at the end of each relationship line, on the ER diagram, represent relationship cardinality and modality. For example, a customer might submit many orders or not submit anything at all, because it's not mandatory for a customer to place an order.

In our ER diagrams (figure 1, page 5), majority of our entities are composed of many attributes. For example, shipping information is included in the customer table. One of the advantages of composing many attributes in one table is that we don't have to do joint queries between different tables. After constructing the ERD, we transformed it into tables. Each table contains one or more primary keys. These keys uniquely identify individual instances of an entity type.

An example is that each customer is uniquely defined by a customer id. Some tables contain referential keys which are a referenced from primary keys of other tables. For example, the customer id from the order table is a referential key from customer id of customer table (figure 2, page 6). Because of the way items are recorded in an order, it would be a simple matter to additional merchandise to the database. It would simply require us to create an inventory table for that type of item and that Item ordered to keep track of the users that order that item. The triggers would have to be updated but no changes would be required to any of the other tables.

Script Files Our group chose to write SQL files to create the tables and to populate them with data. It is possible to create and populate tables by typing in SQL statements at the SQL prompt. However, this makes it very cumbersome to alter the tables when mistakes are made. So, our group decided to create files using a text editor, which contained SQL commands to create our tables and triggers, and then saved it with a '. SQL' extension.

Once the file is created, the 'Start' command, followed by the file name, was used to run and execute the file. When a 'Start' command is executed, each statement in the file is executed in order. Errors occurring in the file are displayed, and the file continues to run. By creating files, our group could easily incorporate changes. All we had to do was edit the commands in our files, and run the files again. For example, if we wanted to add another attribute to our books table, then we would only add in the name of that column into our 'create table' command rather than creating the table all over again.

However, we would have to make sure there is an entry for that column for each book. But since the books are stored in a file, we only have to add in the entry to the existing information of each book, instead of entering in the books all over again. The files also serve as a backup. For example, if the tables got destroyed, all we would have to do is run our files again, instead of creating the tables all over, and then populate them with information. Also, if another group was testing whether they could write into our tables, and the information they wrote destroyed our table, we don't have to panic about creating the table over. Instead it would take us less than a minute to fix the problem.

If we need to move the tables into another account, we can just run the files in that account. The files help save a lot of time. The files also helped us in populating the tables. We wrote one insert command, which contained the right order of attributes for the books and music. Then we made multiple copies of that line and modified the information according to each book or music item. This method saved time because otherwise we would have the same command many times, and also worry about entering the information in the correct order.

If the information was inserted in an incorrect order, then the same command would have to be entered all over again. Triggers After completing the tedious task of populating our database, we then had to write triggers. Triggers are procedures that execute implicitly whenever a table is modified, or when some user actions or database system actions occur and it does not accept arguments. Oracle executes the triggers when an INSERT, UPDATE, or DELETE command is issued against the associated table. The timing can be BEFORE or AFTER and action. You can associate up to 12 database triggers with a given table.

Database triggers fire with the privileges of the owner, not th...


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