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|
Session 11 Helge Pfeiffer
- First hour: Requirements Engineering
- Second hour: Structural Modeling
- Third hour: Behavioral Modeling
- Fourth hour: Feedback
Next week, we will have a guest lecture about GDPR and privacy by design. To motivate that lecture and to motivate the first topic of today, we conduct this task.
- What precisely do you know about your users?
- Where do you have to check?
- Inspect your data model, i.e., all entities on what you store about your users.
- Is there somewhere else to check?
- With a database browser, investigate what your database really contains about users.
Next week, we will have a guest lecture about GDPR and privacy by design.
But why does it matter at all?
<style scoped> section { font-size: 22px; } </style>
- Functional requirements These are statements of services the system should provide, how the system should react to particular inputs, and how the system should behave in particular situations. In some cases, the functional requirements may also explicitly state what the system should not do.
- Non-functional requirements These are constraints on the services or functions offered by the system. They include timing constraints, constraints on the development process, and constraints imposed by standards. Non-functional requirements often apply to the system as a whole rather than individual system features or services. Source: I. Sommerville Software Engineering
requirement
statement which translates or expresses a need and its associated constraints (3.1.7) and conditions (3.1.6)
Note 1 to entry: Requirements exist at different levels in the system structure.
Note 2 to entry: A requirement is an expression of one or more particular needs in a very specific, precise and unambiguous manner.
Note 3 to entry: A requirement always relates to a system, software or service, or other item of interest. Source: ISO/IEC/IEEE 29148:2018(en) Systems and software engineering — Life cycle processes — Requirements engineering
software requirements specification (SRS). (1) documentation of the essential requirements (functions, performance, design constraints, and attributes) of the software and its external interfaces Source: IEEE 1012-2016 IEEE Standard for System, Software, and Hardware Verification and Validation, 3.1.29
Image source: I. Sommerville Software Engineering
Image source: I. Sommerville Software Engineering
-
Read today's project description for implementing the new un-/follow feature of Chirp!.
-
Discuss with your neighbors: What kind of requirement is specified there?
-
In next week's guest lecture, we will realize that the Chirp! application has to be General Data Protection Regulation (GDPR) compliant.
-
Discuss with your neighbors: What kind of requirement is this?
There are multiple ways to perform authentication via third parties (here via GitHub). The lecture and the book present: a) Idendity Core, see ticket #XYZ b) Idendity Core with GitHub OAuth ...
The project task provides a code snippet for the Razor view. It illustrates that there has to be a link that initiates the authentication functionality, which has to contain the text login and which is located in the navigation bar.
... Code example from task comes here ...... More description that you deem necessary ...
Acceptance Criteria:
- There is a link with text
logindisplayed in the navigation bar of Chirp! - If logged into GitHub in another browser window/tab and after clicking the
loginlink, a user is authenticated to Chirp!. - After authentication, a cheepbox appears above the list of cheeps, see ticket #XYZ.
- After authentication, the
loginlink in the navigation bar turns into a link tologoutdisplaying the textlogout. - After clicking logout, the cheepbox disappears again from the top of the list of cheeps.
Eventually, you have to document your system's design and architecture so that your colleagues, customers or other stakeholders have a chance of understanding how your system is structured and how it works.
Remember Martin's guest lecture from two weeks ago? He said that he believes it is the most important task that you have.
Since it is such a common task, various visual notations were developed over time. One of them is the Unified Modeling Language (UML). I will give you a whirlwind tour through some of its diagram types today.
But why do we need a Unified Modeling Language?
Drawback of own notation:
- What is the meaning of note symbols?
- What is the meaning of rounded rectangles?
- What is the meaning of color?
- Separation of concerns/single responsibility? The diagram mixes structural with behavioral concerns?
Best practice:
- You have to provide a legend together with your visualization.
- It it has to describe all used symbols and their meaning.
Best practice:
- You have to provide a legend together with your visualization.
- It it has to describe all used symbols and their meaning.
public class Student
{
public string Name;
public Image photo;
private List<int> courses;
public void enroll(int courseID)
{
courses.Add(courseID);
}
}
public class Student
{
}
public class GuestStudent : Student
{
}
public class Student
{
public string Name;
public Image photo;
private List<Course> courses;
public void enroll(Course course)
{
courses.Add(course);
}
}
public class Course
{
public int Id;
}
If you have bi-directional references in your code, then the association becomes just a line, i.e., no arrows, with the names of the respective references at the opposite end of the association.
For documentation, do not overuse UML class diagrams.
Likely, it is best to use them to illustrate your domain model, i.e., your entities and their relations.
- Navigate to https://app.diagrams.net/.
- From the UML elements in the bottom left, choose classes, associations, and if necessary inheritance relations.
- Draft an illustration of the domain model of your Chirp! application.
- Once done, send an image to our Teams chat (all in one thread), so that we can discuss some of the diagrams.
- Note, the above is likely not a complete entity diagrams once you decide to implement an un-/follow feature to your systems.
What are alternatives to entity diagrams with UML class diagrams?
- ER diagrams as you saw them in your database class.
namespace Chirp.CLI.SimpleDB;
public interface IDatabaseRepository<T>
{
public IEnumerable<T> Read(int? limit = null);
public void Store(T record);
}namespace Chirp.CLI.SimpleDB;
using CsvHelper;
using System.Globalization;
public sealed class CSVDatabase<T> : IDatabaseRepository<T>
{
...
}
A software element that conforms to a standard component model and can be independently deployed and composed without modification according to a composition standard. Source: W.T. Councill et al. "Definition of a Software Component and Its Elements."
A software component is a unit of composition with contractually-specified interfaces and explicit context dependencies only. A software component can be deployed independently and is subject to composition by third parties. Source: C. Szyperski "Component Software: Beyond Object-Oriented Programming"
The component is an independent executable entity that is defined by its interfaces. You don’t need any knowledge of its source code to use it. It can either be referenced as an external service or included directly in a program.
The services offered by a component are made available through an interface, and all interactions are through that interface. The component interface is expressed in terms of parameterized operations, and its internal state is never exposed. Source: I. Sommerville Software Engineering
Discuss with each other, what are components in your Chirp! applications?
- Architecture in the small is concerned with the architecture of individual programs. At this level, we are concerned with the way that an individual program is decomposed into components.
- Architecture in the large is concerned with the architecture of complex enterprise systems that include other systems, programs, and program components. These enterprise systems may be distributed over different computers, which may be owned and managed by different companies. Source: I. Sommerville Software Engineering
@Helge: Name what maps to components in the small and in the large.
[A] Node is a deployment target which represents computational resource upon which artifacts may be deployed for execution. Source: uml-diagrams.org
In your cases, you can consider each service that you receive from Azure as a Node.
- States can be state of your entire application, of some of its components, etc.
- Below is the state of a user of your application. From a starting state (black dot), a user's state transitions between the two states
LoggedInandLoggedOut.
- Note, likely a state machine diagram does not map directly to code in the same way that the class diagram for your domain model does, at least not for your Chirp! applications.
- Initial state
- Activity. Can be anything from what is done in a single method all the way up to long running (even manual) processes.
- Condition (◇)
- Final state
An example of sequence of activities for sending (sharing) a cheep could look like. Note, in your implementations, activities might be in a different order or different activities.
Again, activities do likely map to larger parts of your source code, e.g., controller methods in C♯, Razor views, etc.
Can be used as screen transition diagrams that may be used during design of user centered flow of screens.
Note, the following is an incomplete activity diagram.
- Read again today's project description for implementing the new un-/follow feature of Chirp!.
- Navigate to https://app.diagrams.net/.
- From the UML elements in the bottom left, choose activities, conditions, and start and end states.
- Draft an activity diagram that illustrates a sequence of activities when a user is choosing to follow another user.
public class Student
{
public string Name;
public Image photo;
private List<Course> courses;
public Status enroll(Course course)
{
courses.Add(course);
return Status.Sucess;
}
}
public class Manager
{
private List<Student> students;
public void SignUp(string Name, Course course) {
student = students.Where(s -> s.Name == Name).First();
student.enroll(course);
}
}
You saw a quite complex diagram that was inspired by sequence diagrams already earlier. It illustrates the sequence of calls between different systems in OAuth authentication.
Note, sub-system sequence diagrams are more abstract than "normal" sequence diagrams. The former are on the level of (sub-)systems and the latter on the level of objects (in terms of object-orientation).
What did we do in the previous slides?
- There are two major concerns of a system that you want to illustrate:
- Structure: UML class diagrams
- Behavior: UML statecharts, activity diagrams, sequence diagrams
| Group | Comment |
|---|---|
| 1 | I cannot login with Github |
| 2 | I cannot login via GitHub. After login, I have to register an email address and no cheep box appears? |
| 3 | I cannot login via GitHub. After login, I have to register a username/email address and no cheep box appears? |
| 4 | I cannot register via GH OAuth. I can login via GH but no cheepbox appears? |
| 5 | I cannot login via GitHub. I cannot login via Identity Core. Registration seems to work. |
| 6 | Via Identity Core, my username is my email? After login, no cheepbox appears? |
| 7 | I cannot login via GitHub. After login, I have to register an email address and no cheep box appears? |
| 8 | I cannot login via GitHub. My cheeps are only displayed on my timeline not on the public timeline? Cheeps can be longer than 160 characters? |
| 9 | I cannot cheep from my timeline, why not? I cannot login via Identity Core. Registration seems not to work. |
| 10 | I cannot register via GH OAuth. (Username '[email protected]' is already taken.) |
| 11 | I cannot cheep from my timeline, why not? I cannot logout when logged in via GH? I cannot login via Identity Core. Registration seems to work. |
| 12 | I cannot login via GitHub. After login, I have to register an email address and no cheep box appears? Cheeps can be longer than 160 characters? |
| 13 | I can neither login via Identity Core nor via GitHub OAuth. Cheepboxes appear without being logged in. |
| 14 | I cannot login via GitHub (Error's Timeline). |
| 15 | I cannot login via GitHub. Cheeps can be longer than 160 characters? |
| 16 | No running application? |
| 17 | I cannot cheep from my timeline, why not? |
| 18 | I can neither login via Identity Core nor via GitHub OAuth. |
| 19 | I cannot login via GitHub. (Exception) |
| 20 | ✓ |
| 21 | I cannot login via GitHub (Error's Timeline). I cannot login via Identity Core. Registration seems to work. |
| 22 | I cannot cheep from my timeline, why not? Why am I a "cutie" when trying to send a long cheep? :) |
| 23 | I cannot cheep from my timeline, why not? Cheeps can be longer than 160 characters? I cannot register/login via Identity Core? |
| 24 | I can neither login via Identity Core nor via GitHub OAuth. |
| 25 | ✓ |
| 26 | I cannot login via GitHub. I cannot cheep from my timeline, why not? Why are Adrian's cheeps listed in my private timeline when I am user "A"? |
| 28 | No running application? |
| 29 | I cannot login via GitHub. I cannot login via Identity Core. Registration seems not to work. |
| 30 | No running application? |
| 31 | No running application? |
Let's agree on the requirements:
- An author on your Chirp! application has always a name and an email address.
- An email address is not the name.
- For login: be specific if you want the user to insert a name or an email address.
- When logging in via GitHub OAuth, a user shall not provide an extra email or username. If you need this in your Chirp! application receive this from GitHub with the help of the information that you receive in the ClaimsPrinciple. It should contain a GitHub user ID.
Where should you validate that a cheep is maximal 160 characters long?
a) Via a constraint on the view code? b) Via a constraint on the data model? c) Via a constraint on the endpoint?
How to handle too long cheeps?
a) Prevent a user from sending them? b) Accept them but truncate them?
Consider the principle of least surprise when taking a decision.
The same that is deployed in production. That is, no longer a single executable if this is not deployed like that.
-
From now on, tasks in project work are formulated more openly.
-
That is, you have to analyze what is written there to be able to design a suitable solution and to implement it correctly.
-
If the illustration tools that were presented today help you in analyzing project descriptions and designing suitable solutions, then use them.
We will start the lecture with a guest lecture.
Jakob Krabbe Sørensen from ComplyCloud will give a guest lecture on "Privacy by Design" and why GDPR matters to you as software engineers.
-
If not done, complete the Tasks (blue slides) from this class
-
Check the reading material
-
Work on the project
-
We are done reading chapters from Andrew Lock ASP.NET Core in Action, Third Edition!