F28SD: You are required to develop a series of design models for a software-based access control system. The system is to be called the Secure Occupancy System: Introduction to Software Engineering Coursework, HWU, UK

University Heriot-Watt University (HWU)
Subject F28SD: Introduction to Software Engineering

An Exercise in Designing a Software-Based System: From requirements through to design-level models

You are required to develop a series of design models for a software-based access control system. The system is to be called the Secure Occupancy System. The remit for SOS is described informally below:

SOS shall allow authorized individuals to access a building. Three categories of individuals shall be recognized by SOS, i.e. i) an essential staff member, ii) a non-essential staff member and, iii) a guest (i.e. someone that is not a staff member). Operationally, SOS shall interact with three existing external software systems, i.e. i) the Staff Records System (SRS), ii) the Archive Access System (AAS) and, iii) the Security Monitoring System (SMS). SOS shall maintain a record of all individuals that access the building. For staff members, it shall record their staff ID (SID) and the time at which they enter and exit the building. For guests, it shall record their name, affiliation, and the SID of the staff member that is hosting their visit. The times when a guest enters and exits the building should also be recorded respectively.

All external access points to a building shall be equipped with a keypad. All the keypads shall be connected only to SOS. These keypads support only two access modes, i.e. staff-access and guest-access. If staff-access mode is selected by an individual then a 4-digit SID is requested followed by a 4-digit PIN. Only when both the SID and PIN have been entered and validated is access to the building granted.

In the case of guest-access mode, an 8-digit one-time-code (OTC) is requested. Access to the building is conditional on the 8-digit OTC being valid and the staff member hosting the guest already being in the building. SRS holds details of all staff members and guests and can provide these details on demand, with the exception of the PIN information. For example, if X denotes a valid SID, then retrieve(X) returns the staff category associated with X, i.e. essential or non-essential. Crucially, SOS shall use SRS to validate the various access codes that it receives via the keypads. That is when SOS supplies
SRS with both a SID and PIN, SRS will respond to SOS by confirming whether or not the two codes are valid, i.e. SID is a valid staff ID and the PIN provided is correct with respect to the given SID.

If SOS supplies instead of an OTC, SRS will confirm if it is valid by returning the SID of the associated host. Non-essential staff shall not be allowed to enter a building before 08:00 each day while guests shall not be allowed to enter before 09:00. If any non-essential staff or guests are in the building at 22:00 then SOS shall generate a security alert, i.e. send a message to SMS. The message should contain the names of all the individuals that are no longer authorized to be in the building.

If any individual enters or exits the building outside the core hours of 08:00-22:00 then SOS shall send a message to SMS naming the individual. At 23:59 each day the SOS archives its records of all individuals that have entered and/or exited the building during the previous 24-hours. This archiving process shall involve SOS sending the appropriate
records to AAS. Once AAS has acknowledged receiving the records, SOS shall delete its own copy.

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