ACE GARAGE CASE

Ace Garage Case



Ace Garage Case

Introduction

The aim of this assignment is to produce a single systems design report based on The Ace Garage case. A logical data structure for the Ace Garage Management system has been created in which I have defined the entity, attributes and relations between the tables with the diagram. The Ace Garage is owned by Mr. T. Ford, managed by Mike Spanner. The direct external entities are the Actors, namely three trained Mechanic, two receptions / Book-keeping, one Trainee / Apprentice mechanic & one Cleaner.

Logical Data Structure

Logical data structures are data models, and are sometimes called entity-relationship (ER) models or even entity-attribute-relationship models. (Date 2009 290)

Logical data structures are models which look both ways - at the real world and at the database world. LDSs show the underlying structure of data in the real world. Once we have derived an LDS we then have a map of the data structures which must exist in the database.

Customers of Ace are presently high street retail outlets or shops within shops (aka concessiosn). Ace has around 1000 very active customers and around 2000 who place orders fairly rarely.

Data items

Comments / Description

Customer Account Number

Assigned by the Accounts department when creating a new customer account.

Name

Customer's trading name

Invoicing Address

(used by Accounts only)

Accounts Telephone Number

(used by Accounts only)

Delivery Address

The default delivery address

Credit Limit

Credit Limits are set by the Accounts department

Discount

Allocated subjectively by the Sales Team Leader, depending on sales turnover to the customer.

Normal Buyer Name

Telephone Number

The telephone number of the normal buyer

In our example of a track garage, it is clear that in a given application there may be a large and variable number of tracks to deal with. To permit the realization of sets of objects of the same kind, ACE provides the construct of the linear structure (figure). A linear structure consists of a series of linked garages, with each garage holding in a reserved system word, called the next link, the base address of the next member of the set. The next link of the last garage of a linear structure has the value zero, indicating that there is no next garage. (Codd 2004 102)

A simple linear structure

Example of loop over linear chain

LTK = LFIRST ! Address of the first garage

10 IF (LTK.EQ.0) GO TO finished ! No next garage left ?

..... ! Process data for the garage at LTK

LTK = LQ(LTK) ! Get the address of the next garage

GO TO 10 ! Loop

The next link is stored in the word LQ(LTK) of the garage, with the vector LQ in offset EQUIVALENCE to the vector Q and IQ, as explained later. The example above shows the ACE equivalent of a Fortran DO-loop to process all the garages of a linear structure.

Garages are created dynamically at execution time, and because each garage has one word to connect the rest of the structure of which it is a member, the linear structure permits the creation at execution time of sets of an arbitrary number ...