Requirements and boilerplates Tor Stålhane IDI / NTNU

Content Requirements specifications Why are requirements specification difficult Templates – boilerplates and guided natural language Guided natural language – GNL Boilerplates Boilerplate examples How to communicate requirements – use cases and beyond

Requirements specification

Goal tree – 1

Goal tree – 2

Goal tree – example

Goal description

Why are requirements difficult

What is the problem Effects of Inadequate Requirements development – Airbus: Requirement: Reverse thrust may only be used, when the airplane is landed. Translation: Reverse thrust may only be used while the wheels are rotating. Implementation: Reverse thrust may only be used while the wheels are rotating fast enough. Situation: Rainstorm – aquaplaning Result: Crash due to overshooting the runway Problem: erroneous modeling in the requirement phase

The challenge The main challenges in Requirements Engineering for large systems are that: There are many requirements – often several thousands. Several requirements are interdependent Requirements are related to two or more of: Hardware – computers, sensors, actuators, machinery Software – control, measurement, logging Operators – procedures, behavior

Brake by Wire System – 1 Requirement - Natural language: moving Requirement - Natural language: On a blocked wheel the brake shall be released within 100ms, while the vehicle is moving.

Brake by Wire System – 2 WSS = Wheel Sped Sensor

Templates Boilerplates and Guided Natural language

Humans and machines – 1 Given the amount and complexity of RE, we need to automate as much as possible. Humans and machines have different strong and weak points. We want to elicit and analyze requirements in a way that allows both parties to build on their strong sides.

Humans and machines – 2 We have focused on the differences between man and machine for requirements elicitation and formulation – understanding, observing and reasoning and requirements analysis – memory, information processing and consistency Area Man Machine Understanding Good at handling large variations in written material Bad at handling large variations in written material Observation General observations, multifunctional patterns Specialized observations, quantitative data Reasoning Inductive, slow, imprecise but with good error correction capabilities Deductive, fast, precise but with bad error correction capabilities Memory Innovative, general access Copying, formal access Information processing Single channel, less than 10 bits per second Multichannel, several megabits per second Consistency Unreliable, gets tired, depends on learning Consistent, do not get tired, repeating several actions Force Low level, maximum 1500 watt High level over a long time period Speed Slow, reaction times in seconds Extremely fast

Humans and machines – 3 Machines are good at observing quantitative data and being deductive, fast and precise. In addition, they are good at doing consistent repetition of several actions. bad at handling variations in written material and pattern recognition. Humans are good at handling variations in written material, being inductive. In addition, they are good at doing error correction.

Motivation for use of templates – 1 Text has the advantage of unconstrained expression. There is, however, a need for common Understanding of concepts used to express the requirements and relations between them. Format of presentation Lack of common understanding makes requirement specifications expressed as free text prone to ambiguous representations and inconsistencies. TDT 4242

Motivation for use of templates – 2 Template based textual requirements specification (boilerplates) will introduce some limitations when representing requirements but will also reduce the opportunity to introduce ambiguities and inconsistencies. Boilerplates Provides an initial basis for requirements checking Are easy to understand for stakeholders compared to more formal representations TDT 4242 18

Requirements – 1 There are three levels of requirements: Informal – e.g. Natural language (NL): free text, no rules apply Semiformal Guided Natural Language (GNL): free text but allowable terms are defined by a vocabulare Boilerplates (BP): structured text and an ontology – vocabulary plus relationships between terms Formal: e.g. state diagrams or predicate logic TDT 4242 19

Requirements – 2

Template based textual BPs and GNL – 1 Template based textual = Semantics Syntax + + Meta Model Keywords: Reflects requirement, system and domain concepts RMM Refinement Specialization Guided RSL Boilerplates Analysis Correctness Completeness Consistency Safety analysis Requirements expressed on templates Uses predefined templates based on concepts, relations and axioms to guide requirements elicitation Example: The <system function> shall provide <system capability> to achieve <goal> Requirements expressed using a vocabulary guide Uses predefined concepts, relations and axioms to guide requirements elicitation Example: The ACC system shall be able to determine the speed of the ego-vehicle. Ontology: General and SP specific Requirements classification System attributes Domain concepts

BPs and GNL – 2 Guided Natural Language and Boilerplates will reduce variation and thus giving the machines the opportunity to do what they are best at: to be fast, precise and consistent. By combining humans and machines and let both do what they are best at, we get a better result than we would get if we left the job of handling requirements to just one of them.

Why BPs and GNL – 3 The final goal is to allow the machine to assist the developers in analysing requirements for: Consistency – no requirement contradicts an other requirement Completeness – all necessary requirements are stated Safety implications – consider the possibility for hazards

Guided Natural language

What is GNL - 1 Free text requirement elicitation with the assistance of prescribed words from a dictionary. This will give us requirements which use all terms in a uniform way, thus reducing misunderstandings No formal constraints Requires minimal expertise.

What is GNL - 2 Bridge the gap between unconstrained expression and quality checking when representing requirements as free text. Quality measures: Correctness Consistency Completeness Un-ambiguity (reduced variability) Provide the basis for semantic processing and checking of requirements. Dictionary – Simple taxonomy or more formal ontology

Ontologies – 1 Ontologies are an important part of CESAR's approach to requirements engineering. An ontology has three parts a thesaurus a set of relationships between terms in the thesaurus rules for making interferences based on these relationships. The information used to build an ontology is in our case mainly found in standards and glossaries.

Ontologies – 2 Ontology = Thesaurus + Inference Rules Thesaurus – Domain concepts: entities, terms and events Inference Rules – Relations, attributes and axioms Causality, similarity, reflexivity, transitiveness, symmetric, disjoint (contradiction) …

Ontologies – 3 Required Activity Knowledge capture: Information embedded in domain events from domain experts and ontologist Implementation: Formal representation of captured knowledge. Language: OWL, Support environment: Protégé. Verification: Checking that represented ontology is correct using Classifiers/reasoners Domain experts (semantic accuracy) Mapping of requirement segments to ontology concepts

Ontologies – example Boiler-tank infers Feeding-pump Non-return valve … Water-level Boiler-tank Feeding-pump Non-return valve Tank Max-limit Pump infers has is controlled by Min. water level Max. water level Water-level indicator On Off Control-system has-state is coupled with

Boilerplates

What is a boilerplate – 1 The concept of boilerplates was originally suggested by Hull et al. There is one boilerplate template for each type of requirements, e.g. the <system> shall be able to <action> to <entity> the <system> shall not allow <user> to <action>.

What is a boilerplate – 2 Boilerplates is a set of structures that can be used to write requirements. They use high-level concept classification and attributes TDT 4242

Boilerplate attributes

Main part – 1

Main part – 2 The main thing to be achieved by the requirement, e.g. "…<system> shall <action>” ”…<system> shall allow <entity> to be <state>”

Prefix – 1

Prefix – 2 Prefixes are used to state: The condition under which the action part of a requirement should be executed, e.g. "While <state>…“ "If <event>…“ The rational or goal of the requirement, e.g. “In order to <action>...”

Suffix – 1

Suffix – 2 A suffix is used to describe: Sequencing – e.g. “...before <event>” Exceptions – e.g. “...except for <action>” Timing – e.g. “...within <number> <unit>” Repetitions – e.g. “...at least <quantity> times per <unit>”

Using the boilerplates The RE process is as follows: Select a boilerplate or a sequence of boilerplates. The selection is based on the attributes that need to be included and how they are organized – fixed terms. If needed, identify and include mode boilerplates – prefixes Instantiate all attributes A boilerplate consists of fixed terms and attributes. It may, or may not, contain one or more modes.

Boilerplates in CESAR The original set of boilerplates had an ad-hoc structure and several of them were difficult to combine into more complex requirements. The CESAR project has an on-going process where Project partners use the current set of boilerplates to write requirements for safety critical systems and report problems back to the boilerplate working group – NTNU, Infineon and TU Vienna The boilerplate working group meet when necessary to solve reported problems and issue new boilerplates and update existing ones.

Boilerplate structure A complete boilerplate requirement consist of a prefix, a main part and a suffix. An example of a complete boilerplate requirement is shown below. Even though this requirement is in a semi-formal form it is still easy to read. If <temperature reaches max temperature>, the <boiler controller> shall <reduce the power to the heating unit> within <2> <seconds>.

Ontologies and boilerplates The full potential of using boilerplates for requirements will only be realized when we combine them with one more ontologies. We can then: Check the completeness of the requirements in relations to a given ontology. E.g. if we are using the steam-boiler ontology and do not have a requirement for a safety valve, the tool will tell you that the requirements are not complete and, if inquired, will tell you that it expects one or more safety valve requirements. Enforce a consistent use of terms, just as for GNL. E.g. in the steam boiler ontology, the terms tank and vessel will be replaced by the term boiler-tank.

Boilerplate examples - 1 The <user> shall be able to <capability> Attributes: <user> = driver <capability> = <verb> <entity> = start the ACC system Requirement The driver shall be able to start the ACC system TDT 4242

Boilerplate examples - 2 The <system> shall be able to <action> <entity> Attributes: <system> = ACC system <action> = <verb> = determine <entity> = the speed of the ego-vehicle Requirement The ACC system shall be able to determine the speed of the ego-vehicle TDT 4242

Boilerplate examples - 3 Prefix: While <state> Main part: <user> shall be able to <capability> Attributes <state> = activated <user> = driver <capability> = override engine power control of the ACC system Requirement While activated the driver shall be able to override engine power control of the ACC-system TDT 4242

Non-functional requirement example – 1 Non-functional requirements and soft goals fits into the same BPs as functional requirements The <system> shall be able to <action> to <entity> Suitability: The <system > shall be able to <provide an appropriate set of functions> to <the user> TDT 4242

Non functional requirement example – 2 Non-functional requirements and soft goals fits into the same BPs as functional requirements The <system> shall be able to <capability> …for a period of at least <quantity> <unit> Maturity: The <system > shall be able to <operate without failure> for a sustained period of at least <quantity> <time unit> TDT 4242

Non functional requirement example – 3 While <state> The <system> shall be able to <action> <entity> While <normal state> the <system> shall be able to <tolerate> <90% of software faults of category...>

Summing up The use of boiler plates and ontologies will Enforce a uniform use of terms Reduce the variability of presentations – requirements that are similar will look similar Reduced variation in form and contents simplifies the use of automatic and semi-automatic tools for Checking requirement quality – e.g. completeness and consistency Creating test cases

User stories

Why user stories User stories is another way to use templates. Boilerplates define the terms to use User stories define the required content

What is a User Story Stories are used as: A concise, written description of a piece of functionality that will be valuable to a user (or owner) of the software. Stories are used as: Descriptions of user’s needs Product descriptions Planning items Tokens for a conversation Mechanisms for deferring conversation

User Story Cards have three parts Description - A written description of the user story for planning purposes and as a reminder Conversation - A section for capturing further information about the user story and details of any conversations Confirmation - A section to convey what tests will be carried out to confirm the user story is complete and working as expected

User Story Template – 1 Example: As a [user role] I want to [goal] so I can [reason] As a [type of user] I want to [perform some task] so that I can [reach some goal] Example: As a registered user I want to log in so I can access subscriber-only content

User Story Template – 2 Who (user role) What (goal) Why (reason) gives clarity as to why a feature is useful can influence how a feature should function can give you ideas for other useful features that support the user's goals

From user story to test case We can use templates to write test cases for the use stories. One tool that employs such templates is CUCUMBER: Scenario: a short description of the test scenario Given: test preconditions When: test action – input Then: test result – output And: can be used to include more than one precondition, input or output.

Use stories (US) vs. boilerplates (BP) We can use boilerplates to formulate use stories US: As a [user role] I want to [goal] so I can [reason] BP: The [user role] shall [action] in order to achieve [goal] US: As a [type of user] I want to [perform some task] so that I can [reach some goal] BP: The system shall be able to [perform some task] in order to achieve [some goal]

Boilerplate examples

SafeLoc – 1 Robot rail Position switch Robot arm Robot platform Light emitter Light receiver Gate B Gate A Area A Area B Fence Restart switch

SafeLoc – 2 if <state>, <system> shall <action> within <quantity> <unit> if <gate is opened to the zone where the robot is operating>, <robot control> shall <stop> <robot> within <10> <milliseconds>, <system> shall not allow <entity> to be <state>, unless <state> <robot control> shall not allow <robot> to be <started>, unless <all gates are closed> and <reset button is pushed> TDT 4242

SafeLoc – 3 If <event>, <system> shall <action> if <robot moves into an occupied zone>, <robot control> shall <stop> <robot>

ACC requirements – 1 The minimum selectable time gap for steady state vehicle following shall be greater than or equal 1s for all speeds. At least one time gap tau in the range 1.5s to 2.2s shall be provided <ACC> shall not allow <driver> to <set> <time gap less than 1s> <ACC> shall be able to <select> <at least one time gap tau> within <1.5 to 2.2> <seconds> The ACC system shall be able to determine the speed of the ego-vehicle <ACC> shall be able to <determine > <the speed of the ego-vehicle> An ACC system is not required to respond to stationary targets. If the system is not designed to respond to stationary targets the driver shall be informed at least by a statement in the vehicle owner’s manual <ACC > may <response> <to stationary targets> If <ACC does not respond to stationary targets>, <ACC manual> shall <inform> < driver>

ACC requirements – 2 The ACC system shall enable steady state vehicle following on (a) straight roads (class I, II, III and IV) and (b) curves with a radius down to 500m (class II, III and IV), down to 250 m (class III and IV), and down to 125m (class IV) <ACC> shall be able to <steady state vehicle following> on {<straight roads class I, II, III and IV> and < curves with a radius down to 500m on roads class II, III and IV> and <curves with a radius down to 250 m roads class III and IV> and <curves with a radius down to 125m on roads class IV>}   An ACC system shall provide means for a driver to select a desired set speed <driver> shall be able to <select> <desired speed> The driver shall always have the authority to override the ACC system engine power control <driver> shall be able to <override> <ACC engine power control>

Heating unit – system overview Temperature sensor Heating element 220V AC Controller I/O panel

Natural language requirements The user shall be able to use a simple panel to define time intervals, consisting of Starting time Ending time Temperature during this interval – Ta The time intervals are not allowed to overlap The user shall be able to use a simple panel to define a temperature tolerance value d. If the user don't set a temperature tolerance, the system shall use default value d = 2oC If the temperature falls below Ti – d, the heather shall be turned on If the temperature exceeds Ti + d, the heather shall be turned off If time is outside all defined intervals the temperature shall be set to a predefined default value T0.

Boilerplate requirements – 1 <user> shall be able to <define> <time interval a = [ts, te]> <system> shall not allow <time intervals> to <overlap> <user> shall be able to <set> <temperature Ta for time interval a> <user> shall be able to <set> <temperature tolerance d> If <temperature tolerance not set>, <system> shall <set> <temperature tolerance = 2> <system> shall have <simple input / output panel> <system> shall have <heating unit> <system> shall have <default temperature = T0> In order to <measure temperature>, <system> shall have <temperature sensor>

Boilerplate requirements – 2 In order to <control temperature>, <heating unit> shall have <on / off switch> If <temperature sensor reading exceeds T + d>, <system> shall <switch on heating unit> If <temperature sensor reading is below T - d>, <system> shall <switch off heating unit> When <time in [ts, te] for interval a>, <system> shall <set> <T = Ta> <system> shall <sample> <temperature sensor> at least <3> times per <minute> <system> shall not allow <time intervals> to <overlap> If <time is outside all time intervals>, <system> shall <set> <T = T0>

How to communicate requirements Use cases and beyond

Finding use cases Describe the functions that the user wants from the system Describe the operations that create, read, update, and delete information Describe how actors are notified of changes to the internal state of the system Describe how actors communicate information about events that the system must know about TDT 4242

Key points for use cases - 1 Building use cases is an iterative process You usually don’t get it right at the first time. Developing use cases should be looked at as an iterative process where you work and refine. Involve the stakeholders in each iteration TDT 4242

Reuse opportunity for use cases – 1 There is duplicate behavior in both the buyer and seller which includes "create an account" and "search listings". Extract a more general user that has the duplicate behavior and then the actors will "inherit" this behavior from the new user. TDT 4242

Reuse opportunity for use cases – 2 Relationships between use cases: Dependency – The behavior of one use case is affected by another. Being logged into the system is a pre-condition to performing online transactions. Make a Payment depends on Log In Include – One use case incorporates the behavior of another at a specific point. Make a Payment includes Validate Funds Availability TDT 4242

Reuse opportunity for use cases – 3 Relationships between use cases: Extends – One use case extends the behavior of another at a specified point, e.g. Make a Recurring Payment and Make a Fixed Payment both extend the Make a Payment use case Generalize – One use case inherits the behavior of another; it can be used interchangeably with its “parent” use case, e.g. Check Password and Retinal Scan generalize Validate User TDT 4242

Extend Respond to emergency Control center operator communication down <<extends>> Request arrives through radio or phone

Generalize Request (re)scheduling of maintenance Maintenance worker Already scheduled - reschedule Proposed time not acceptable Maintenance worker Ask for new suggestion Changes in time consumption or personnel

Adding details We can add details to a use case diagram by splitting uses cases into three types of objects. Entity object Control object Boundary object

Adding details – example Input and output via boundary objects Validate input and output via control objects Save via entity objects

From UC to SD – 1

From UC to SD – 2

From UC to SD – 3

Use case diagrams – pros and cons Simple use case diagrams are Easy to understand Easy to draw Complex use case diagrams – diagrams containing <<include>>> and <<extend>> are difficult to understand for most stakeholders. Use case diagrams do not show the sequence of actions

Textual use cases - 1 Identify the key components of your use case. The actual use case is a textual representation TDT 4242

Textual use cases - 2 Examples of alternative flow are: While a customer places an order, their credit card failed While a customer places an order, their user session times out While a customer uses an ATM machine, the machine runs out of receipts and needs to warn the customer Alternative flow can also be handled by using <<extend>> and <<include>> TDT 4242

Textual use cases – 3 Most textual use cases fit the following pattern:

Textual use case – example Use case name Review treatment plan Use case actor Doctor User action System action Request treatment plan for patient X Check if patient X has this doctor Check if there is a treatment plan for patient X Return requested document Doctor reviews treatment plan Exceptional paths 2.1 This is not this doctor’s patient 2.2 Give error message This ends the use case 3.1 No treatment plan exists for this patient

Textual use case <<extend>> Use case name Respond to System emergency call Use case actor Operator User action System action System OK => Receive system signal System Down => Use radio Receive system message Act on message Send response End REC – 1 Use case name Respond to radio emergency call Use case actor Operator User action System action Receive radio message Act on message Send response End REC – 2

Textual use case <<include>> Use case name Controller Use case actor NA Start timer Get data Action necessary? Yes => Set Actuator Timer expired ? No => BIT Check error status On => Error handling End Controller Use case name BIT Use case actor NA Get test pattern A Write test pattern Read test pattern Compare patterns Difference => Set error status End BIT

Textual use cases – pros and cons Complex textual use cases Are easier to understand than most complex use case diagrams Are easy to transform into UML sequence diagrams Require more work to develop Show the sequence of actions