Reuse is a major theme in software engineering practices. By reusing tried-and-tested components, the robustness of a new software system can be enhanced while reducing the manpower and time requirement. Reusable components come in many forms; it can be reusing a piece of code, a subsystem, or a whole software.
While you may be tempted to use many libraries/frameworks/platform that seem to crop up on a regular basis and promise to bring great benefits, note that there are costs associated with reuse. Here are some:
One of your teammates is proposing to use a recently-released “cool” UI framework for your class project. List the pros and cons of this idea.
Note that having more cons does not mean we should not use this framework. Further investigation is required before we can make a final decision.
An Application Programming Interface (API) specifies the interface through which other programs can interact with a software component. It is a contract between the component and its clients.
The GitHub API is a collection of Web request formats GitHub server accepts and the corresponding responses. We can write a program that interacts with GitHub through that API.
When developing large systems, if you define the API of each components early, the development team can develop the components in parallel because the future behavior of the other components are now more predictable.
Choose the correct statements
(a) (c) (d) (e)
Explanation: (b) is incorrect because private methods cannot be a part of the API
Defining component APIs early is useful for developing components in parallel.
Explanation: Yes, once we know the precise behavior expected of each component, we can start developing them in parallel.
An API should be well-designed (i.e. should cater for the needs of its users) and well-documented.
When we write software consisting of multiple components, we need to define the API of each component.
One approach is to let the API emerge and evolve over time as we write code.
Another approach is to define the API up-front. Doing so allows us to develop the components in parallel.
We can use UML sequence diagrams to analyze the required interactions between components in order to discover the required API. Given below is an example.
As we analyze the interactions between components using sequence diagrams, we discover the API of those components. For example, the diagram above tells us that the MSLogic component API should have the methods:
More details can be included to increase the precision of the method definitions before coding. Such precision is important to avoid misunderstandings between the developer of the class and developers of other classes that interact with this class.
Preconditions are the conditions that must be true before calling this operation. Postconditions describe the system after the operation is complete. Note that post conditions do not say what happens during the operation. Here is another example:
A library is a collection of modular code that is general and can be used by other programs.
Java classes you get with the JDK (such as
HashMap, etc.) are library classes that are provided in the default Java distribution.
Natty is a Java library that can be used for parsing strings that represent dates e.g.
The 31st of April in the year 2008
built-in modules you get with Python (such as
sys, etc.) are libraries that are provided in the default Python distribution. Classes such as
dict are built-in library classes that you get with Python.
Colorama is a Python library that can be used for colorizing text in a CLI.
These are the typical steps required to use a library.
The overall structure and execution flow of a specific category of software systems can be very similar. The similarity is an opportunity to reuse at a high scale.
IDEs for different programming languages are similar in how they support editing code, organizing project files, debugging, etc.
A software framework is a reusable implementation of a software (or part thereof) providing generic functionality that can be selectively customized to produce a specific application.
Eclipse is an IDE framework that can be used to create IDEs for different programming languages.
Some frameworks provide a complete implementation of a default behavior which makes them immediately usable.
Eclipse is a fully functional Java IDE out-of-the-box.
A framework facilitates the adaptation and customization of some desired functionality.
Eclipse plugin system can be used to create an IDE for different programming languages while reusing most of the existing IDE features of Eclipse. E.g. https://marketplace.eclipse.org/content/pydev-python-ide-eclipse
Some frameworks cover only a specific components or an aspect.
JavaFx a framework for creating Java GUIs. TkInter is a GUI framework for Python.
More examples of frameworks
Although both frameworks and libraries are reuse mechanisms, there are notable differences:
Libraries are meant to be used ‘as is’ while frameworks are meant to be customized/extended. e.g., writing plugins for Eclipse so that it can be used as an IDE for different languages (C++, PHP, etc.), adding modules and themes to Drupal, and adding test cases to JUnit.
Your code calls the library code while the framework code calls your code. Frameworks use a technique called inversion of control, aka the “Hollywood principle” (i.e. don’t call us, we’ll call you!). That is, you write code that will be called by the framework, e.g. writing test methods that will be called by the JUnit framework. In the case of libraries, your code calls libraries.
Choose correct statements about software frameworks.
Explanation: While both libraries and frameworks are reuse mechanisms, and both more concrete than principles and patterns, libraries differ from frameworks in some key ways. One of them is the ‘inversion of control’ used by frameworks but not libraries. Furthermore, frameworks do not have to be bigger than libraries all the time.
Which one of these are frameworks ?
Explanation: These are frameworks.
A platform provides a runtime environment for applications. A platform is often bundled with various libraries, tools, frameworks, and technologies in addition to a runtime environment but the defining characteristic of a software platform is the presence of a runtime environment.
Technically, an operating system can be called a platform. For example, Windows PC is a platform for desktop applications while iOS is a platform for mobile apps.
Two well-known examples of platforms are JavaEE and .NET, both of which sit above Operating systems layer, and are used to develop
Enterprise Application: ‘enterprise applications’ means software applications used at organizations level and therefore has to meet much higher demands (such as in scalability, security, performance, and robustness) than software meant for individual use.
Cloud computing is the delivery of computing as a service over the network, rather than a product running on a local machine. This means the actual hardware and software is located at a remote location, typically, at a large server farm, while users access them over the network. Maintenance of the hardware and software is managed by the cloud provider while users typically pay for only the amount of services they use. This model is similar to the consumption of electricity; the power company manages the power plant, while the consumers pay them only for the electricity used. The cloud computing model optimizes hardware and software utilization and reduces the cost to consumers. Furthermore, users can scale up/down their utilization at will without having to upgrade their hardware and software. The traditional non-cloud model of computing is similar to everyone buying their own generators to create electricity for their own use.
Cloud computing can deliver computing services at three levels:
Infrastructure as a service (IaaS) delivers computer infrastructure as a service. For example, a user can deploy virtual servers on the cloud instead of buying physical hardware and installing server software on them. Another example would be a customer using storage space on the cloud for off-site storage of data. Rackspace is an example of an IaaS cloud provider. Amazon Elastic Compute Cloud (Amazon EC2) is another one.
Platform as a service (PaaS) provides a platform on which developers can build applications. Developers do not have to worry about infrastructure issues such as deploying servers or load balancing as is required when using IaaS. Those aspects are automatically taken care of by the platform. The price to pay is reduced flexibility; applications written on PaaS are limited to facilities provided by the platform. A PaaS example is the Google App Engine where developers can build applications using Java, Python, PHP, or Go whereas Amazon EC2 allows users to deploy application written in any language on their virtual servers.
Software as a service (SaaS) allows applications to be accessed over the network instead of installing them on a local machine. For example, Google Docs is an SaaS word processing software, while Microsoft Word is a traditional word processing software.
Google Calendar belongs to which category of cloud computing services?
Explanation: It is a software as a service. Instead of installing a calendar software on your desktop, we can use the Google Calendar software that lives ‘on the cloud’.