1.10.2003Software Engineering 2004 Jyrki Nummenmaa 1 A BASIC OO SOFTWARE DEVELOPMENT PROCESS Earlier, we saw a number of different software lifecycle models

1.10.2003 Software Engineering 2004Jyrki Nummenmaa

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A BASIC OO SOFTWARE DEVELOPMENT PROCESS

• Earlier, we saw a number of different software lifecycle models.

• Similarly, there exists different ways to develop object oriented (OO) software.

• We will start with a very basic OO waterfall model as given in the textbooks. That model is ok, if there is no (relational) database and the software is not that big.

• Later, we will study why this is typically only good for small non-database software.

• We will also study how large-scale database-driven OO software should be developed.


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The Waterfall Model for OO

• The same model basically applies with V&VRequirement specification

Maintenance

Testing

Implementation

Analysis & Design

<- This is standard.

<- This is the main thing.

<- This is done according

to the design.This has some special issues, but I will talk --->about testing separately.

We may talk about this separately. ->


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Object Analysis And Design

• The goal is to start from the requirements, and to come up with a description of the software (classes with their attributes and methods) which can be implemented in a fairly straightforward way.

• Usually we talk about “analysis model” and “design model”.

• Analysis model is something which, in principle, describes the system in OO terms, but we would not want to implement it as such, for reasons such as efficiency and maintainability.

• Design model is something we want to implement.


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Object Analysis

• Goal: Start from the requirement specification and come up with – A description of the classes (commonly a class diagram, to be

introduced later)– A description on how the use cases are to be executed using

these classes (with some other UML diagrams such as sequence diagrams, also to be introduced later).

• Methods:– “Meditation-type” methods which more or less means “no

methods”.– Requirement specification text analysis. <- Our plan here!– Analysis of all possible technical documentation of an old system

or other existing systems.– Possibly separate analysis of the domain (e.g. banking).


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OBJECT ANALYSIS

• Although there is some variance, most methods are based on what is called OMT (Object Modeling Technique).

• I present a simplified technique, which follows the main ideas of most of these methods.

• I will present the technique using an example, which I have modified from ”Oliokirja” by Kai Koskimies.

• The example is a simplified version of the famous Finnish board game ”Afrikan tähti” (African Star).

• I will explain the various types of diagrams as they are needed.


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Object Design - Architecture

• This typically starts with something called “architectural design”, which in a way describes the basic solutions and or models, which the design is going to follow.

• Here, we identify different processes, which possibly run on different computers.

• There is a number of “design styles”, which may be applied.

• The technology and the software development tools may probably have a major impact on the architectural solutions.


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Object Design

• Once the architectural decisions have been made, the analysis model is developed into a model describing the classes that we are actually going to implement.

• The UML diagram types are probably mostly the same as in analysis, but new classes, methods and attributes are introduced for the implementation.


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Object Analysis Goals/Phases

1. Identify classes.2. Create a vocabulary, which is updated

continuously.3. Identify associations.4. Identify responsibilities.5. Identify operations (methods)6. Identify attributes7. Create inheritance structure8. Check and clean-up


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Example Board Game Requirement Specification / 1

The game shall be implemented as a computer application with a graphical user interface. The game is played by two or more players. Each player has a playing piece, which all look different. The pieces are moved on the playing board. When the game starts, all pieces are in starting place and each player recieves a sum of game money. The game has a set of places, on which the pieces can be positioned. The places are either ordinary places or special places. Some pairs of these places are connected by a connection. Graphically, the connections form paths on the board. There are flight connections for some pairs of places.

The players take turns to play. The game includes a dice, which shows how many steps each playing piece is to be moved in each turn. With each step, the players’ piece is moved from one place to another place using a connection on condition that these places are connected. A player may use a flight connection by paying one unit game money, assuming he is at one end of the flight connection when his/her turn comes.


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At the start of the game, each special place has a card face down. When a player arrives to a special place, he/she may pay one unit game money to take the card (which can only be taken once). Alternatively, the player may stay on a special place, and instead of moving, throw the dice for trying to take the card: dice values 4,5, and 6 mean the player gets the card.

The card may be a bandit, meaning the player loses all money, a jewel with a value, meaning that the player receives money for that value, or a treasure. The treasure may not be sold, but if another player arrives to a place which has a player with the treasure, the arriving player gets the treasure. When a player with the treasure arrives to the starting place, that player wins the game and the game ends. The game boards, places, pieces, labels, connections, etc. each have a graphical representation in the user interface, but that representation is not specified here.


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Use Case ”Start”

Name: StartVersion: 1.0Summary: The game is initialisedFrequency: Once per every game playedUsability Requirements:Actors: Players, the game applicationPreconditions:.Descriptions: The game application shows a dialogue, where all player’s names are typed in. The game application randomly chooses the game pieces for the players and the order in which players take turns. The game starting position is initialised by putting the pieces in the start place and randomly choosing the cards for the special places. Postconditions:Exceptions:


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Sequence Diagrams for Use Cases

• Sequence Diagrams show interaction between actors.• The use cases may be drawn into sequence diagrams, which

show the interaction between users and the system.• The sequence diagrams are fairly self-evident at this point:

we have two actors (the official term is ”classifier role” for sequence diagrams) and the arrows show the communication.

• The arrows represent (asynchronous) message passing or (synchronous) method calls.

• Based on the sequence diagrams, it is possible to identify a set of tasks, which the system is to perform.


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User

Application

Choose start

Ask player names

Player names

Show pieces

Show initialised board

Sequence Diagram for ”Start”

- Vertical lines stand for actors (here ”User” and ”Application”)- Time runs down in the diagram- Arrows show interaction/operations


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Use Case ”Take Card”

Name: Take CardVersion: 1.0Summary: A player takes a cardFrequency: Probably not as often as once every roundUsability Requirements:Actors: A player, the game applicationPreconditions: It is the player’s turn, the player has money, and the player is in a special place with a card that has not been taken.Descriptions: The player chooses to take the card. One unit money is taken from the player. The card is a jewel, and the player’s funds are increased with the respective amount of money. Postconditions:Exceptions:


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User

Application

Choose to take card

Show player’s funds with one unit taken

Show Card

Show player’s funds with jewel value added

Sequence Diagram for ”Take Card”


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Use Case ”Flight”

Name: FlightVersion: 1.0Summary: A player flies from one place to anotherFrequency: Probably not as often as once every roundUsability Requirements:Actors: A player, the game applicationPreconditions: It is the player’s turn, the player has money to fly, and the player is in a place, where there are flight connections.Descriptions: The player chooses to fly. The player is shown the possible destinations, of which the player chooses one. The game application moves player’s piece to the chosen destination, and his funds are decremented by one unit. Postconditions:Exceptions:


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User

Application

Choose to fly

Show possible destinations

Choose destination

Show position

The flow continues in usecase ”Take card”

Sequence Diagram for ”Flight”


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Use Case ”Stepping”

Name: SteppingVersion: 1.0Summary: A uses a playing turn to move with the diceFrequency: Most players do this on most roundsUsability Requirements:Actors: A player, the game applicationPreconditions: It is the player’s turn.Description: The player uses the dice. The game application shows

the result and the possible places to move to. The player chooses one, which is a special place with a card that has not been taken. The game application moves player’s piece to the new place. ”Take Card” use case follows.

Postconditions: Exceptions:


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User

Application

Choose to use the dice

Show result and possible destinations

Choose destination

Show position

The flow continues in usecase ”Take card”

Sequence Diagram for ”Stepping”


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StartStart

FlightFlight

SteppingStepping

Take cardTake card

Board Game

Player

<<include>>

<<include>>

Board Game Use Case Diagram


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Analysis model: Classes

• Text analysis• Go through the text, and pick nouns


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Nouns from Requirement Spec. (let’s hope I got them right :)




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Nouns from Requirement Specification / 2

At the start of the game, each special place has a card face down. When a player arrives to a special place, he/she may pay one unit game money to take the card (which can only be taken once). Alternatively, the player may stay on a special place, and instead of moving, throw the dice for trying to take the card: dice values 4,5, and 6 mean that the player gets the card.



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Nouns from Use Case ”Start”

Name: StartVersion: 1.0Summary: The game is initialisedFrequency: Once per every game playedUsability Requirements:Actors: Players, the game applicationPreconditions:.Descriptions: The game application shows a dialogue, where all player’s names are typed in. The game application randomly chooses the game pieces for the players and the order in which players take turns. The game starting position is initialised by putting the pieces in the start place and randomly choosing the cards for the special places. Postconditions:Exceptions:


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Nouns from Use Case ”Take Card”

Name: Take CardVersion: 1.0Summary: A player takes a cardFrequency: Probably not as often as once every roundUsability Requirements:Actors: A player, the game applicationPreconditions: It is the player’s turn, the player has money, and the player is in a special place with a card that has not been taken.Descriptions: The player chooses to take the card. One unit money is taken from the player. The card is a jewel, and the player’s funds are increased with the respective amount of money. Postconditions:Exceptions:


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Potential classes

game computer player(game) piece (game) board path(game) money dice stepturn place dice valuespecial place card banditjewel treasure starting placerepresentation user interface flight connectionconnection (jewel) value unitconnection pair (of places) amount (of

money) (computer) application


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Reasons for rejecting potential classes

• irrelevant• in essence same as some other class• a likely attribute or a value• a likely method• a control-related concept• a role of another class• an association between classes• vague• implementation-specific


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Alternatively: Conditions For Accepting a Class

These are typicallychecked by examining an object of that class.1. Retained information – the system needs some information

about object to function.2. Needed services – the object has operations, which change its

attribute values.3. Multiple attributes (a single-attribute class seems like a

”minor” thing at this stage).4. Common attributes (a set of attributes, which apply to all

objects of the class.5. Common operations (like with attributes above)6. Essential requirements – external entities, which consume or

produce information will almost always be modeled as objects in the analysis model.


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Rejected classes

• computer, computer application (irrelevant)• board (represents the same thing as path) ->

in fact, we choose to use ”map” for both of them• amount, amount of money (a likely attribute)• game money, dice value (a likely value for an attribute: a

class is probably not needed)• step (a likely operation)• turn (control-related)• starting place (a role for place)• representation (irrelevant)• jewel value (a likely attribute)• pair of places (represents the same thing as connection)• unit (irrelevant)• bandit, jewel (value) – treasure is a bit of a question mark!


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Classes

card connection diceflight connection map piece place player special placetreasure game


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PiecePiece

GameGameSpecial placeSpecial place

TreasureTreasurePlayerPlayer

DiceDice

MapMap CardCardPlacePlaceFlight

connectionFlight

connection

An Initial Class Diagram

The classes are drawn as rectangles.However, we do not have any associations between classes.Nor do we have any operations or attributes.

ConnectionConnection


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A Model Vocabulary

• The names are not generally that descriptive.• It is a good idea to make a model vocabulary for all

words that appear in the model as names.• It will be natural to start from the class names

once they have been identified.• The vocabulary should be updated, when new

names are identified.


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Initial Vocabulary (actually just a part of it, but you get the idea)

Bandit A possible symbol to appear on a card. If a player takes a card, and the card is found to have a bandit, the player loses all of his/her funds.

Dice Randomly returns one of values 1, 2, 3, 4, 5 or 6. The return value is used to showing how many steps a player may advance or, alternatively, if a player gets to take card for free, in which case at least 4 is required.

Game piece Each player has a game piece, which is used to show the position of the player. Every game piece looks different.

…

…


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Task list

• Once the use case sequence diagrams have been produced, they are analysed for forming a task list.

• Each arrow from the user to the application represents a service requested from the application.

• Each arrow from the appliction to the user represents an output from the application.


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Task List For The Game Application

• Initialise game• Showing board, piece positions, funds, and game status• Showing dice result• Showing a set of destination places• Choose to use the dice• Choosing to fly• Choosing to start a game• Choosing to open a card• Choosing a destination from a set of places • Ask player names• Input player names


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Associations

• Associations are relationships, references, and dependencies between classes.

• In practice, they can be found in sentences, which represent relationships between classes.

• Examples of types of associations:– location – control – communication– inclusion– and so on…


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Potential Associatons / 1




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At the start of the game, each special place has a card face down. When a player arrives to a special place, he/she may pay one unit game money to take the card (which can only be taken once). Alternatively, the player may stay on a special place, and instead of moving, throw the dice for trying to take the card: dice values 4,5, and 6 mean the player gets the card.



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Some potential associations

(1) The game is played by players(2) Player has a playing piece(3) Pieces are in starting place -> Piece is in a place(4) Pieces are moved on the playing board(5) Game has (a set of places) -> map(6) Places are connected by a connection(7) Connections form paths on the board(8) Places are either ordinary places or special places(9) Game includes a dice(10) Player may use a flight connection (11) Player is at one end of the flight connection (12) Special place has a card (13) Player throws the dice(14) Player has the treasure


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Reasons for rejecting associations

• An association may be trivial.• An association may be irrelevant.• An association may be follow from other

associations.• An association may turn out to be a momentary

action. In this case we may find an operation.• An assocation may relate several classes, and it

should be split into binary associations.• We may have an inheritance instead of

association.• Common sense should be used.


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Rejecting Associations

(1) The game is played by players(2) Player has a playing piece(3) Piece is in a place(4) Pieces are moved on the playing board - activity(5) Game has a map(6) Places are connected by a connection –>

map contains places and connections(7) Connections form paths on the board – map info(8) Places are either ordinary places or special places

- inheritance(9) Game includes a dice(10) Player may use a flight connection - activity (11) Player is at one end of the flight connection (3)(12) Special place has a card (13) Player throws the dice - activity(14) Player has the treasure


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Association names

(1) The game is played by players -> play(2) Player has a playing piece -> uses (3) Piece is in a place -> located(4) Game has a map -> has(5) Places are connected by a connection

connect(6) Map contains places and connections

-> contains(7) Game includes a dice -> includes(8) Special place has a card -> Card covers

special place(9) Player has the treasure -> owns


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Association names

(1) player–play–game(2) player-use-piece -> uses (3) piece-located-place -> are(4) game-has-map -> has(5) connection-connect-places -> we decide to

to make connection an association betweenplace and place: place-connected-place

(6) map-contain-places (7) game-include-dice(8) card-cover-special place(9) player-own-treasure


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Association details

• Find good and short names for associations.• Add extra specifications, such as

- Navigation direction,- Aggregation information,- Ordering information,- Multiplicity specifications, and- Qualifiers (used to identify objects of target end of the association)


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uses owns

located

include

contains

play

{ordered}

cover end

0..1 0..1

0..1

2

*

*

*

**

*

connected

PiecePiece

GameGame Special placeSpecial place

TreasureTreasurePlayerPlayer

DiceDice

MapMap CardCardPlacePlaceFlight

ConnectionFlight

Connection

1

1

11

1

0..10..1

1

Classes And Associations

The little numbers at the ends of associations are cardinalities.


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Some Observations This Far

• This is not a deterministic process: two analysts may well – and probably will – come up with two different analysis models.

• We use common sense in many places.• There are no strict rules, only guidelines. The

better you know what you are doing, the less you are bound by the guidelines.

• At any time, we may find that it is better to change something in the model. Just be aware of the consequences.


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Class Responsibilities

• Now it may be a good time to have a thought about why the classes are there.

• In other words, what is the role of each class in the analysis model of the system.


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Example Class Responsibilities

Piece Maintains player’s position on the map.

Dice Gives a random number from {1,2,3,4,5,6}, where each value

has equal probability.

……


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Applying Classes to Sequence Diagrams

• Now it will be a good time to edit our sequence diagrams.

• The sequence diagrams are to use the classes in the class diagram.

• We specify the flow of operations from class to class (actually, of course, it will be from object to object).


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User Player

Choose to take card

Show funds

Card Value

Sequence Diagram for ”Take Card”

Game

Pay (1)

Updated funds

Place Card

Turn Card

Value

Get Value

Show card value

Add Funds (Value)

Show funds


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Identify Operations

• Operations now come primarily from three sources:- The sequence diagram (since we have no asynchronous message passing here, each arrow represents a call).- The requirement specification: the potential operations are likely to be verbs.- The task lists collected earlier on (This one is actually just a double check – all of these should be in the sequence diagrams.)


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Some Operations For Class Player

• From the previous sequence diagram we get : Pay(value: Integer):Integer and AddFunds(value:Integer):Integer.

• From the requirement specifications we get:getPlace():Place, hasMoney(value:Integer):Boolean,moveTo(p:Place), hasTreasure():Boolean, takeTreasure(t:Treasure), giveTreasure(t:Treasure),isWinner():Boolean,canFly():Boolean


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Identify Attributes For Classes

• Attributes now come from various sources.• We may find from the requirement specification,

that some attribute is vitally important for some class, like the amount of money for a player.

• Also the sequence diagrams may imply a need for an attribute, like the name of a player.

• At this point we want to record the attributes that are clearly important for the model.

• We may want to avoid such implementation-specific attributes, which may well change, once we make a more detailed model.


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More Detailed Representation For Class In A Class Diagram

• A box with three compartments: Header, Attributes, and Operations. We are still missing some details.

Player

name: Stringmoney: Integer

Pay(value: Integer):Integer AddFunds(value:Integer):Integer getPlace():Place hasMoney(value:Integer):BooleanmoveTo(p:Place)hasTreasure():Boolean takeTreasure(t:Treasure)giveTreasure(t:Treasure)isWinner():BooleancanFly():Boolean


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Inheritance Structure

• Is some class a special case of another class?• Do we have some kind of a division into different

subtypes?• A compound noun (consisting of more than one

words) may indicate inheritance.• Do we have classes, which seem to share

properties?• Would it be useful to use some generally known

wider concept? (Like bandit -> criminal – in this case the answer is no, we do not need this generalisation.)


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Example Inheritance

• In our example, Special Place is clearly a Place.

Place

Special Place


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User Interface Specification

• Now would be a good time to make a first version of the user interface specification, unless it already exists.

• Nowadays the user interface is typically graphical.• In fact, many books just talk about GUI (Graphical

User Interface) in the understanding that by default the user interfaces are graphical.


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Final Check-Ups / 1

• Is everything necessary?• Do we need more classes?

If, for instance, the classes and attributes in a class do not all seem to belong together, it might be good to split the class.

• Is everything consistent? Have we taken care of all the knock-on effects that our changes have created.- As an example, if we have split a class into two, have we updated the sequence diagrams accordingly? And if so, do these changes imply more changes, and have these changes been done accordingly?


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Final Check-Ups / 2

• Does the model seem sufficient? (Does it include all relevant concepts and associations?)

• Does the model seem understandable?• Is the model easy to read? Are the names chosen

correctly?• Have we avoided redundancy? (One thing only

done once.)• Does the model really describe the target system?• If all of the above is fine, then we have created the

analysis OO model of our system!

Documents

1.10.2003Software Engineering 2004 Jyrki Nummenmaa 1 A BASIC OO SOFTWARE DEVELOPMENT PROCESS Earlier, we saw a number of different software lifecycle models