The table Signup depicts a one-table database recording the enrolment informatio

Question

The table Signup depicts a one-table database recording the enrolment information of sports club members in sports activities. The information recorded are the member id, the member name, the activity id, the activity name, a session id that is unique within the same activity, the day, start and end times of the activity session enrolled, and the id and name of the coach supervising the activity session. Each session must be supervised by only one coach and the duration of all activity sessions is one hour.

Signup (MemberID, MemberName, ActivityID, ActivityName, SessionID, Day, From, To, CoachID, CoachName)

a) Write down a set of functional dependencies that covers all the non-trivial dependencies in this scenario. You need to be especially careful in this step.

Explanation / Answer

A basic objective of the first normal form defined by Codd in 1970 was to permit data to be queried and manipulated using a "universal data sub-language" grounded in first-order logic.[8] (SQL is an example of such a data sub-language, albeit one that Codd regarded as seriously flawed.)[9] The objectives of normalization beyond 1NF (First Normal Form) were stated as follows by Codd: 1. To free the collection of relations from undesirable insertion, update and deletion dependencies; 2. To reduce the need for restructuring the collection of relations as new types of data are introduced, and thus increase the life span of application programs; 3. To make the relational model more informative to users; 4. To make the collection of relations neutral to the query statistics, where these statistics are liable to change as time goes by. —E.F. Codd, "Further Normalization of the Data Base Relational Model"[10] The sections below give details of each of these objectives. [edit] Free the database of modification anomalies An update anomaly. Employee 519 is shown as having different addresses on different records. An insertion anomaly. Until the new faculty member, Dr. Newsome, is assigned to teach at least one course, his details cannot be recorded. A deletion anomaly. All information about Dr. Giddens is lost when he temporarily ceases to be assigned to any courses. When an attempt is made to modify (update, insert into, or delete from) a table, undesired side-effects may follow. Not all tables can suffer from these side-effects; rather, the side-effects can only arise in tables that have not been sufficiently normalized. An insufficiently normalized table might have one or more of the following characteristics: The same information can be expressed on multiple rows; therefore updates to the table may result in logical inconsistencies. For example, each record in an "Employees' Skills" table might contain an Employee ID, Employee Address, and Skill; thus a change of address for a particular employee will potentially need to be applied to multiple records (one for each of his skills). If the update is not carried through successfully—if, that is, the employee's address is updated on some records but not others—then the table is left in an inconsistent state. Specifically, the table provides conflicting answers to the question of what this particular employee's address is. This phenomenon is known as an update anomaly. There are circumstances in which certain facts cannot be recorded at all. For example, each record in a "Faculty and Their Courses" table might contain a Faculty ID, Faculty Name, Faculty Hire Date, and Course Code—thus we can record the details of any faculty member who teaches at least one course, but we cannot record the details of a newly-hired faculty member who has not yet been assigned to teach any courses except by setting the Course Code to null. This phenomenon is known as an insertion anomaly. There are circumstances in which the deletion of data representing certain facts necessitates the deletion of data representing completely different facts. The "Faculty and Their Courses" table described in the previous example suffers from this type of anomaly, for if a faculty member temporarily ceases to be assigned to any courses, we must delete the last of the records on which that faculty member appears, effectively also deleting the faculty member. This phenomenon is known as a deletion anomaly. [edit] Minimize redesign when extending the database structure When a fully normalized database structure is extended to allow it to accommodate new types of data, the pre-existing aspects of the database structure can remain largely or entirely unchanged. As a result, applications interacting with the database are minimally affected. [edit] Make the data model more informative to users Normalized tables, and the relationship between one normalized table and another, mirror real-world concepts and their interrelationships. [edit] Avoid bias towards any particular pattern of querying Normalized tables are suitable for general-purpose querying. This means any queries against these tables, including future queries whose details cannot be anticipated, are supported. In contrast, tables that are not normalized lend themselves to some types of queries, but not others. For example, consider an online bookseller whose customers maintain wishlists of books they'd like to have. For the obvious, anticipated query—what books does this customer want?—it's enough to store the customer's wishlist in the table as, say, a homogeneous string of authors and titles. With this design, though, the database can answer only that one single query. It cannot by itself answer interesting but unanticipated queries: What is the most-wished-for book? Which customers are interested in WWII espionage? How does Lord Byron stack up against his contemporary poets? Answers to these questions must come from special adaptive tools completely separate from the database. One tool might be software written especially to handle such queries. This special adaptive software has just one single purpose: in effect to normalize the non-normalized field. Unforeseen queries can be answered trivially, and entirely within the database framework, with a normalized table.

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