System modeling is a technique to express, visualize, analyze and transform the architecture of a system. Here, the Access Control System consist of software components, hardware components, or both and the connections between these components. A system model is then a skeletal model of the system.
System modeling is intended to assist in developing and maintaining large systems.
System modeling can increase reliability and reduce development cost by making it easier to build systems, to reuse previous built components within new systems, to change systems to suit changing requirements such as functional enhancement and platform changes, and to understand systems. In this way, a system model can satisfy different requirements such as documenting the system, providing a notation for tools such as consistency checkers and can also be used in the design stage of system development.
Thus, system modeling is used to ensure that a developing piece of software evolves in a consistent manner and that the task of integrating software components is simplified.
Let us take as example a large building of about 20 floors of a particular organization. You will agree with us that the Chief executive floor cannot be accessible to every staff in the organization nor visitors and as such there is a need for a proper access rights to different floors in the building.
To solve this problem, we can make use of an Access Control System.
The Access Control System will control access to a building by giving proper access rights to authorize staff. Each staff will have a card through which the latter will gain access to a particular floor / floors.
The model architecture is shown below. Solid boxes indicate external system components and the arrows indicate information flows.
Click on image to enlarge
Overview of the system
External System Components
Payroll System
Since access and exit time are being monitored by the access control system, the payroll system will get that information and use to calculate the salary of staff working in the organization.
HR System
Every staff will have an id card created by the access control system with a unique id number and their picture. This information is very important as far as HR planning is concerned.
Fire Alarm System
The access to different floors is control by the access control system, in the event of a fire; the fire alarm system will send information to the access control system so that all doors in the building are immediately open so as to allow a quick evacuation of the building.
CCTV System
Due to the fact that the access control system contain a database of all the employees working in the organization , the CCTV system can make use of the database to quickly identify an employee.
Internal System Components
The Access Control (Main Server)
It is the heart of the system; it coordinates all the information and communication flow among the internal system components as well as the external system components.
Access Database
All the information regarding the system is stored in the access database e.g. information about employees, information about the configuration of different devices in the system.
Backup Processor
Very important, as in the event the system fails all the backup database can be used to quickly restore the system.
Master Controller
The master controller receive information from other controllers and pas it on to the main server. All processing is done by the main server and the master controller pass information to the relevant slave controllers.
Slave Controller
It receive information from the master controller and convey it to the devices e.g. card reader… it also receive information from the devices and forward it to the master controller.
Id card Design & Activation
Each employee will receive a card which will be activated (access to a predefined number of floors in the building)
Time and Attendance processor
Based on the time of access and exit of employees a time and attendance can be process.
Component | Description | Function |
Controller | Electronic communication card | Act as an interface between main computer and different devices |
Manual door open opener | Push button | Allows a door to open without the use of a card |
Card Reader | Electronic device | Read a predefined card and allow or denied access |
Door sensor | Electronic device | Detect if a door has been properly closed |
Door latch | Motorized device | Look or unlock a door |
Assume that a new employee is recruited to work in the building as accounts officer. A picture of the employee is taken and entered in the access control. His card is design and activated to have access to the office of accounting found on level 12.
The latter will have access to that level only. Every time the later enter the office he will have to swipe his card at the card reader located on each floor to have access.
Suppose now that the new employee has to meet a friend working on level 10, but due to the fact the new employee does not have access to that floor, fortunately he will!!. His friend working on level 10 will make use of the manual door opener (which can be a small push button ) to open the door and meet the new employee.
If a door is left open or not closed properly , the door sensor will relate this information to the slave controller which forwards it immediately to the access control processor via the master controller and the operator will be notified and thus remedial action can be taken.
These are properties of the system as a whole rather than properties that can be derived from the properties of components of a system.Emergent properties are a consequence of the relationships between system components.They can therefore only be assessed and measured once the components have been integrated into a system.it can divided into 2 parts :
1.Non-functional emergent properties
( General properties of the system
Exist regardless of how well the system is functioning
Tolerable ranges are usually given, or assumed (speed, reliability) )
Volume (Memory, hard disk space; how does it scale with use (saved data))
The system can offer an optional Redundancy Server
with a mirror database which monitors all data activity on the
primary server and creates a real-time copy of the
system database. In the event of primary server failure, the mirror
database automatically launches the Redundancy Server which
supports all the features and functionality of the primary server.
Once the primary server returns online, all archives are merged
and/or the entire database is copied from the Redundancy
Server.
Reliability (Depends on hardware, software, operators)
The system architecture supports connections to remote sites using Ethernet. It is a multi-workstations it also supports connections to remote sites using TCP/IP
(communication servers) or dial-up modems.
Security (vulnerable to attack? Who has access?)
The system will have different level of security . Different users can be defined e.g Administrator, Operator .... so as to keep the integrity of the system. Moreover an action or query made by a user is recorded by the system. So that any malicious tampering in the system can be easily located.
Speed (Depends on underlying hardware components)
A networked access control system is a necessity with today’s global companies. The system makes it much more cost-effective to have such a system by including TCP/IP onboard, eliminating the need to use an external communication device to link to the network. Another money-saving feature, onboard TCP/IP eliminates the costs associated with buying and maintaining a third party communication device.
Robustness: (Reacts well to unanticipated use; related to reliability)
Since large building have a standby power generator , electrical power will not be a critical issue ,moreover there will be an online UPS attached to the main system to ensure smooth operation. The controllers will have independent battery backup .
2.Functional emergent properties
( Desirable property that the components are trying to realize only appear when the system is working well
Are usually specified explicitly
May only appear in certain situations
More specific than non-functional properties (Sorts all integer lists vs. reliability) )