LOG8430E: Frameworks and Distributed Systems - Fall 2021 M. Fokaefs et F. Guibault
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LOG8430E: Frameworks and
Distributed Systems
Fall 2021
©M. Fokaefs et F. Guibault
So far…
LOG2410
OO Design
(SOLID)
Styles and Patterns of Distributed
Architectures
Design
Patterns
2
Today
LOG1410
OO Design Styles and Patterns of Distributed Architectures
(SOLID)
Design
Patterns Frameworks
Ecosystems
Pluggable
Architectures
LOG8430 – ©M. Fokaefs et F. Guibault 3
The distributed systems…in the wild!
Definitions Examples Development Maintenance
• Frameworks • AngularJS • The culture • Break the framework
• Plugins • Django • The priorities
• Ecosystems • Eclipse
• Android
• Node.js
• R/CRAN
2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 4
Frameworks: Definition
• The frameworks are architectures half implemented and generic (agnostics
to the application).
• They provide a skeleton with basic functionality intended to be extended.
• In a framework, there are abstract modules (hot spots), which the
developers should extend, and concrete modules (frozen spots), which
should not be changed.
• So, frameworks implement the OCP principle by definition.
• A good example is the Template Method pattern.
• The template method is the concrete part. The abstract methods called by the
template method constitute the part that will be extended.
• For other examples of the use of patterns in frameworks, consult the article: “Meta
Patterns—A Means For Capturing the Essentials of Reusable Object-Oriented
Design”, by Wolfgang Pree.
2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 5
Frameworks: Properties
• Inversion of control: It’s the concrete modules of the framework that
dictate the control flow and the not the modules extended by the
program.
• Also known as the Hollywood principle: “Do not call us, we will call you.”
• One implementation of the DIP principle.
• Example 1: ActionListeners. The framework manages the events of the
graphical interfaces and the code of the developer is notified to provide the
reaction to these events.
• Example 2: The Strategy pattern.
• Extensibility and reusability are increased, but modifiability is
reduced.
2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 6Plugins: Definitions • The plugins follow a “microkernel” architecture (as in the case of operating systems). 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 7
Plugins: Properties
• The basic system is atomic and independent. This means that the
base system can function without plugins.
• The plugins add supplementary functionalities.
• Contrary to frameworks, the plugins improve the experience of the
user more than that of the developer.
• The plugins definitely depend on the base system, but it is possible
that they also depend on other plugins.
• The flexibility and the extensibility are increased, but the
maintainability may suffer.
• The plugins strongly depend on the version of the base system (a form of the
vendor lock-in).
2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 8Software ecosystems
• In fact, a software ecosystem is a collection of modules, which have something in
common, e.g., a language, a framework etc.
• There are numerous definitions that also include business aspects and economic
relationships. Often, an ecosystem is simply a repository of software modules shared by a
community of developers.
• The presence of a platform, as in the case of frameworks or plugins, is not
necessary.
• WARNING! This does not mean that plugins or frameworks are not an ecosystem, but we can
classify these systems in a more concrete fashion.
• The modules, or the “packages”, contribute functionalities.
• The base of the packages is just a language or an execution environment (like
JRE).
• Like the frameworks, but unlike the plugins, the packages facilitate the work of
the developers.
2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 9Ecosystems: Properties • It’s the principal model for open source systems. • The contributions are managed by the community, which specifies the regulations and habits of development and of contribution. • Any contribution is possible, as long as it conforms to the terms and regulations. • The functionalities are separated and isolated. • The modularity, the testability and the reusability are increased. • Maintainability may suffer as in the case of plugins. 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 10
Examples 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 11
AngularJS
• AngularJS is a framework for the development of web applications in
JavaScript.
• The framework follows a MVC architecture.
• It is possible to implement any variant of this style: MVC, MVP, MVVM
• The principles of AngularJS are:
• Less code
• Increased automatization: data association, page transition.
• Increased testability and reusability.
• The disadvantages:
• Poor security
2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 12Architecture of AngularJS 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 13
Django
• Django is a framework for web application development in Python.
• The framework follows a MVT architecture (Model-View-Template).
• The controller is part of Django.
• The Templates are a mix of HTML and DTL (Django Template Language). The
DTL specifies actions or variables in the HTML code of the page.
• The principles of Django
• Low coupling, high cohesion
• Rapid development
• Less code
• SRP guaranteed, cloning is minimized.
• Secure, extensible, coherent.
2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 14Architecture of Django 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 15
Eclipse
• Eclipse is an integrated development environment (IDE).
• Basically, it’s a more sophisticated Java editor.
• Eclipse is a pluggable architecture.
• Additional plugins offer much more capabilities, among others programming in other
languages.
• The plugins use the SDK (Standard Development Toolkit) to add to the
functionality, the interface or both.
• The principal objective of Eclipse is the unification of programming tools under a
single platform.
• Eclipse is officially supported by IBM, but there are numerous companies and
developers that work with the platform.
• 490 contributors from 40 companies worked on the first version.
• Today, there are 1000 contributors from 170 companies.
2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 16Architecture of Eclipse 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 17
Android
• Android is a platform for the development of mobile applications.
• Android is also an operating system for mobile devices.
• In fact, it is a framework, a pluggable architecture and an ecosystem
at the same time.
• The Android applications follow a MVVM architecture.
• Model – Room/Retrofit
• ViewModel – Lifecycle, LiveData
• View - UI
2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 18Architecture of Android 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 19
Architecture of Android Applications 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 20
Node.js • Node.js is an execution environment for JavaScript. • The developers can contribute modules to Node.js in the form of packages. • The packages are managed, installed and configured by npm (Node Package Manager). • Node.js is a platform for the development of server applications, and it is also an ecosystem. • It follows an event-driven architecture. 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 21
Architecture of Node.js 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 22
R/CRAN –
The Comprehensive R Archive Network
• CRAN is a distributed repository for R packages.
• R is a language for scientific calculations and statistics.
• The developers can contribute their own packages in CRAN.
• The community has regulations for the submission of packages.
• CRAN follows a peer-to-peer architecture.
• Distributed servers have duplicated files between them.
• The selection of the server, from which to download a package, is based on
proximity.
2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 23Development and maintenance of distributed systems 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 24
Maintenance of distributed systems
• Statement: The design quality of a software does not play any role in
its functional maintenance.
• True? Two systems with different designs/architectures (e.g.,
monolithic vs modular) can have identical functionality.
• False! The design quality affects the capacity to efficiently maintain
the functionality of the system.
• A flat or complex design can complicate the maintenance, especially in the
case of an external change.
• So, we “clean up” beforehand, so that we can be ready to receive our
“visitors”.
2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 25How to break an API? • Interviews with the developers of three ecosystems (Eclipse, R, Node.js) • Questionnaires with responses from 2000 developers from 18 ecosystems. 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 26
Definitions of the study • Breaking changes: Due to dependencies between the modules that are developed independently, changes can propagate through the ecosystem. • Negotiations of the impact of breaking changes: The strategy of the developers with respect to who is responsible of adapting to changes. 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 27
Eclipse • Value: Backwards compatibility to reduce the cost for users. • Eclipse is updated every year with few breaking changes. • Expensive for maintainers. • Minimal effort and cost for users. • The development is perceived as stagnant. • New contributors are discouraged. 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 28
R/CRAN • Values: Easy for users, rapid access to current research. • The packages in CRAN are synchronized every month. • Medium volume of breaking changes. • The costs are shared between maintainers and users. • Collaboration with external maintainers are encouraged. • The urgency to react to updates can be perceived as an obstacle. 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 29
Node.js • Value: The publication and use of packages need to be easy and fast for developers. • The update of packages is independent and decoupled. • It is the responsibility of the user to update their package based on changes on other packages. • Many breaking changes. • Rapid evolution requires constant maintenance or risk of falling behind. 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 30
So, how to break an API? • Eclipse: not possible. • R/CRAN: communicate with affected developers. • Node.js: increase the number of the major release. 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 31
Which value is the most important one for each ecosystem? 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 32
Frequency of breaking changes 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 33
Coordination between maintainers 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 34
Refrain to evolve due to dependencies 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 35
It’s worth adding a dependency if it will add significant value. 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 36
The frequency of collaboration and communication between the maintainers. 2021-09-06 LOG8430 – © M. Fokaefs et F. Guibault 37
Next time
LOG1410
OO Design Styles and Patterns of Distributed Architectures
(SOLID)
Design
Patterns Frameworks
LOG8371 Ecosystems
Pluggable
Architectures
LOG3430
Design
Quality
LOG8430 – ©M. Fokaefs et F. Guibault 38You can also read
