Software Engineering Methodologies

ITECH7410 - Software Engineering Methodologies

                Assignment 2 – Formal 

               System Specification

Overview

The purpose of this assessment is to provide students with the opportunity to apply knowledge and skills developed during the semester with particular reference to the formal specification of a system through the use of Z notation. Students complete the assignment in groups of two.

As described in this course’s third study guide, Software Analysis, Modelling and Specification, a Formal Specification (Technique) is one that has a rigorous mathematical basis and one of its advantages is that it can be mathematically checked for completeness. The course’s fourth study guide, System and Software Design, also states that by using formal methods it is possible to derive a formal design from a formal specification and then be able to prove that the design and specification are functionally equivalent.

Your text, Software Engineering: A Practitioners Approach (Pressman, 2010) indicates that formal methods provide frameworks that allow people to specify, develop and verify systems in a structured and systematic way and that the mathematical based specification language used in formal methods ensures a greater chance of consistency, completeness and lack of ambiguity in a specification. Pressman also discusses formal specification languages and their common components – syntax, semantics and sets of relations. Of the four formal specification languages he identifies – OCL, LARCH, VDM and Z – he provides useful discussion with respect to OCL and Z.

In this assignment, you will use the Z specification language to provide the sets, relations and functions in schemas to specify the Container Control System (CCS) described below. Your schemas should provide the stored data that the system accesses and alters and identify the operations that are applied to change the state as well as the relationships that occur within the system. Remember, as specified in Spivey’s 2001 text, The Z Notation: A Reference Manual, schemas are utilized to illustrate both static and dynamic aspects of a system. Static aspects include such things as the states a system occupies and the invariant relationships that continue to exist as the system moves between states. Dynamic aspects include the changes of state that occur, possible operations and the relationships between their inputs and outputs. Remember also you should always be conscious of the fact that a specification tries to describe what the system must do without saying how it is to be done (Spivey, 2001).

Keep all the above in mind as you read the following information. You are required to create a set of Z schema that adequately describes the CCS. Your assignment should include at least one state space and provide schema for the prescribed functions (including error handling) described below.

Assessment Details

This assignment will be assessed by your lecturer/tutor. The assignment requires you to produce a formal specification containing the components identified below.

Background – Container Control System (CCS)

As a Software Engineering consultant, your task is to develop a formal specification in Z for the Container Control System (CCS). The CCS is a new computerized system to be developed for the storage and handling of accounts for freight companies and truck container deliveries/pickups to/from the Port of Melbourne (PoM) container terminals.

This system could be quite complicated. However, to simplify the system for this assignment only the following detail will be included in the proposed system (we do not for example track individual containers but only truck deliveries and pickups and ship loading and unloading and we assume one container size only (standard twenty-foot equivalent unit (TEU)):

Container Terminal

The PoM currently has four container terminals in Melbourne but the system must be written to seamlessly handle at least twice that number.

Each terminal has a unique name and storage capacity (in number of containers and tonnes) that must be stored in the proposed system.

The system must maintain the current tonnage and current number of containers in the container terminal.

When the container terminal is full no further deliveries of containers can be made to that container terminal and no unloading of containers from ships can occur before some are loaded onto a ship for shipping to their destination or some are picked up by trucks and taken away from the terminal.

Only five trucks can deliver into a particular container terminal at any one time and only five trucks can pick up containers from the container terminal at any one time. During busy times each container terminal maintains two queues of trucks - waiting to deliver and waiting to pick up.

Trucks wanting to deliver should only be entered into the waiting queue when there is sufficient room in the container terminal for all the container(s) that the truck holds i.e. the system needs to know that the current storage plus all the loads currently in the queue will not exceed the container terminal’s capacity tonnage or number of containers capacity.

For simplicity, we will say that a berth is always available for a ship to load or unload.

A container terminal cannot load more containers onto a ship than are currently stored at the terminal.

A container terminal cannot unload more containers from a ship than there is available space at the terminal.

When a container terminal is loading containers onto a ship, operational and safety considerations dictate that no trucks can deliver any containers to that container terminal (i.e. they must wait in the delivery queue).The system will ensure that all deliveries and pickups currently executing are completed before loading starts.

Similarly when a container terminal is unloading containers from a ship, operational and safety considerations dictate that no trucks can pick up any containers from that container terminal (i.e. they must wait in the pickup queue). The system will ensure that all deliveries and pickups currently executing are completed before unloading starts.

Trucks

The system maintains a list of registered trucks, their registration, owner and their empty weight (in tonnes).

As each loaded truck arrives at the container terminal, it is weighed to ascertain the weight of the containers on the truck. This is calculated as the difference between the weight of the loaded truck and its empty weight. The number of containers on the truck is also registered.

If there is sufficient room in the container terminal then the container(s) are placed in the container terminal and a record is kept of the number and tonnage delivered against both the truck registration number and the freight company providing the container(s).

When container(s) are placed on a truck to take them away from the terminal, the truck is weighed to ascertain the weight of the containers on the truck and the number of containers taken away is also recorded.

Freight Companies

The system will maintain a record of each freight company that assigns trucks to deliver containers to the container terminal and also each freight company that allocates trucks to pick up containers from the terminal.

Details to be kept include the freight company’s name, address and phone number.

Ships

The system will keep a record of all ships that have been registered to load or unload containers for the PoM.

The ship’s name, nationality (flag) and capacity (in number of containers and tonnes) will be stored.

The ship's captain can specify the number of containers and the tonnage to be loaded/unloaded onto/from the ship.

When loading a ship, the number of containers and tonnage to be loaded cannot be greater than the ships capacity and cannot be more than the available number of containers and tonnage in storage. The ship cannot load until all currently executing deliveries and pickups have completed (any new truck deliveries and pickups are placed in the appropriate queue). The system will keep a record of the number of containers and tonnage loaded onto the ship and adjust the remaining storage capacity in the container terminal and ship appropriately.

When unloading a ship, the number of containers and tonnage to be unloaded cannot be greater than the remaining storage capacity in the container terminal. The ship cannot unload until all currently executing deliveries and pickups have completed (any new truck deliveries and pickups are placed in the appropriate queue).The system will keep a record of the number of containers and tonnage unloaded from the ship and adjust the remaining storage capacity in the container terminal and ship appropriately.

Date and Time

Normally the date and time of each operation (truck delivery, truck pick up, ship loading, ship unloading) would be recorded. However to simplify this assignment those aspects will be ignored. Instead, a sequential count of each operation for each container terminal should be kept. Therefore, there should be a history of the order of truck delivery, ship loading, ship unloading and truck pickup operations that take place for each container terminal. There is also a need to keep track of the operation order between terminals. Therefore a global sequential number of the operations at terminals should be kept as well. The system would be able to say for example, that at container terminal SWANSON, count 999 involved the delivery of 2 containers of 3.5 (1.5 and 2.0) tonnes respectively by the truck registered AAA203 (owned by Gunner Myson) from freight company Freight’s Rates. The global operation 12337 at WEBB was a container pickup of 1 container weighing 2.0 tonnes by a truck with registration ABA713 and requested by the On The Way freight company. The next operation at SWANSON, with Global No of 12340 and Count of 1000 was a Pickup of 2 containers weighing 2.5 tonnes for the Container Carriers freight company. Global event number 12338 occured at VICTORIA and it was the un-loading of 2000 containers weighing 3500.0 tonnes from the Southern Star container ship and Global event number 12339 at APPLETON was the loading of the Liberian Princess container ship with 1500 containers weighing in total, 2000.0 tonnes. Sometime and some events later, Global event number 12500 at VICTORIA with a count of 650 was the loading of the Southern Star with 1200 containers at 2500.0 total tonnage.

The following table gives an example of this record of events:

Global No	Container	Count	Operation	Vehicle	Qty	Tonnes	Freight
	Terminal			Identifier			Company
12336	SWANSON	999	Delivery	AAA203	2	3.5	Freight’s
							Rates
12337	WEBB	555	Pickup	ABA713	1	2.0	On The
							Way
12338	VICTORIA	600	Un-Load	Southern Star	2000	3500.0
12339	APPLETON	750	Load	Liberian	1500	2000.0
				Princess
12340	SWANSON	1000	Pickup	QWE810	2	2.5	Container
							Carriers
…	…	…	…	…	…	…	…
12500	VICTORIA	650	Load	Southern Star	1200	2500.0
…	…	…	…	…	…	…	…
...

Assessable Tasks/Requirements

You are to create a set of Z schemas that adequately describes the CCS. It should include at least one state space and the following operations:

•         An initialization operation called Init.

•         An operation Enter_new_container_terminal that an operator uses to enter the details of a new container terminal into the system. Assume the new container terminal is currently empty.

•         An operation Accept_delivery that an operator uses to signal to the system to begin delivery (placing in the container terminal) of x quantity and y tonnes of containers from a truck. Note that the system must do a check to see if that storage capacity is available in the container terminal. If it is not then an error message must be output and no truck delivery occurs. Additional information needed by this routine is the truck registration and the freight company’s name. If successful, this operation stores all necessary details into the system for that delivery. If five trucks are already delivering then this new truck will be placed in a queue waiting for its turn to deliver.

•         An operation Accept_pickup that an operator uses to signal to the system to begin pickup (placing on the truck) of x quantity and y tonnes of containers from the container terminal. Additional information needed by this routine is the truck registration and the freight company’s name. If successful, this operation stores all necessary details into the system for that pickup. If five trucks are already picking up then this new truck will be placed in a queue waiting for its turn to pickup.

•         An operation Leave_delivery_queue. This operation is run by the system operator each time there is a delivery queue for a container terminal and the driver of a specified truck decides that the anticipated waiting time is too long and leaves the queue. The operation outputs to the operator the list of trucks in the queue after the specified truck is removed. If no trucks are left in the queue a reasonable error message should be produced.

•         An operation Unload_ship that an operator uses to signal to the system to begin unloading (placing in the container terminal) of x quantity and y tonnes of containers from the ship. Note the system must check that all deliveries and pickups have stopped before unloading can commence. A suitable message must be output until this has been achieved. The system must also do a check to see if the quantity and tonnage storage capacity is available in the container terminal. If this check fails, then an error message must be output and no ship unloading occurs. (From an operational perspective, the operator may, after consultation, try the operation again with adjusted values to have a successful ‘partial’ unload but you do not need to be concerned with this as the functionality already described would accommodate this process). Additional information needed by this routine is the ship identifier. If successful, this operation stores all necessary details into the system for that unloading.

•         An operation Container_terminal_account that outputs the total number and tonnage of containers delivered to a particular container terminal by ALL freight companies in a specified time period (in this simplified system, that is the total quantity and tonnes delivered between two specified global count values e.g. 10000 and 10500).

•         An operation Ships_total_account that outputs the total number and tonnage that a particular ship has loaded from ALL container terminals in the total history of the system.

•         An operation Freight_company_account that outputs the total number and tonnage of containers delivered to and the total number and tonnage picked up from ALL container terminals for each freight company between two specified global count values.

You should provide robust versions of each operation that are capable of handling any possible error conditions. For example, if the ship or truck is not correctly registered in the system an appropriate error message must be given.

You should also add a narrative to explain any schemas or logic that you have used. Authorship should be made clear. You might be asked to explain and answer questions about your work.

Marking Criteria

Work will be assessed according to the following:

•         Your CCS Formal Specification must complete the items detailed within the Assessable Tasks/Requirements section of this document.

•       Your CCS Formal Specification should be presented as business or management style report which adheres to academic writing presentation standards. Where applicable, it must contain high quality academic presentation, expression and features as outlined in:

o       Federation University’s

§     Assignment Layout and Appearance Guidelines;

§     General Guide to Writing and Study Skills,

§     General Guide to Referencing; and

o       Features of Academic Writing (from UEfAP.com)

Marking Rubric

Student  Name  and		Marker
No
		Date
Item	Description			Max. Marks	Student Mark
Global Variables	Correct declaration and initialisation			5
State Space Schema	Correct declaration and type for variables			5
	Correct predicates
Init Operation	Correct initialisation of variables			5
Enter_new_container	Correct schema for entry, error and success			10
_terminal Operation	Correct robust expression
Accept_delivery	Correct schema for test of available room, successful			10
Operation	delivery, successful queueing and error
	Correct robust expression
Accept_pickup	Correct  schema  for  successful  pickup,  successful			10
Operation	queueing and error
	Correct robust expression
Leave_delivery_queu	Correct schema for removal of truck, list of trucks in			10
e Operation	queue and error
	Correct robust expression
Unload_ship	Correct schema for test of delivery and pickups stopped,			10
Operation	available room, successful unloading, updating of system
	and error
	Correct robust expression
Container_terminal_	Correct declaration and type for variables			10
account Operation	Correct predicates
Ships_total_account	Correct schema for report and error (no ship in system)			10
Operation	Correct robust expression
Freight_company_ac	Correct declaration and type for variables			10
count Operation	Correct predicates
Report	Adheres  to  guidelines  given  for  assignment  (Any			5
	assumptions must be clearly stated and appropriate)

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