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• [nick][✓ char, 2020-10-22]Char review done

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installability and its mirror requirement of un-installability allows for an individual product or an entire system to be installed and uninstalled on a system easily, efficiently and with a minimum number of side effects. A side effect occurs when removing a product or system has adverse effects on other products or systems running on the same computer or network. For example, when a product was installed, it installed a library to access a particular dbms but, in so doing, removed a library required to access a different DBMS. These side effects can also occur when a product or system is un-installed. For example, when a product is un-installed, it removes a library used to access a particular DBMS; however, this library is required by other products or systems on the computer or network.

In addition, the complexity of installing or un-installing a product or system may be extremely tedious, detailed, and laborious with many steps and decision points. Each step in this process introduces risk. It is important to remember that risk is multiplicative, thus as the number of steps involved increases, even if the individual risk of each step is low, the overall risk to the success of the installation or un-installation increases.

Many of these issues were the bane of new systems and products in the past. Fortunately many of these issues have been addressed through the use of Wizards, packagemanager tools, containerization processes and orchestration tools. Installation usually entails the following checks and functions:

• The target system has the correct system resources available

  • Hardware architecture (32-bit or 64-bit cpu etc)
  • os such as Android, IOS, Linux, MacOS, Windows, Unix, etc.)
  • Network connectivity
  • Hardware resources such as memory, disk space, etc.
• The target system does not already have the software installed (i.e., previous or current version of the software). If so, perform an upgrade.
• The target system has the proper directories, files and operating system privileges
• Add configuration data (i.e., configuration files, envvar, or windowsregistry entries) to the target system
• Make software accessible on the target system (i.e., setting privileges, creating links, and shortcuts)
• Configure components required to run the target system (i.e., daemon, services, etc )
• Activate software on the target system (i.e., license agreements, license activation, system registration, etc.)
• Update other third party components to acceptable levels on the target system

Installers can be classified according to the amount of interaction with the user:

In addition to the kinds of installations. Installers programs can either be self contained¹⁾ and specific²⁾ in what they can install (i.e., wizard) or they can be generalized to handle any kind of installation (i.e., packagemanager). Sometimes, installer programs themselves need to be installed or updated, a pattern referred to as "bootstrapping", which entails the use of a lightweight, simple and small executable file that is initially downloaded and started on the target system. This executable updates the installer software and then launches into the installation of the desired software. Often in complex systems or programs, the initial bootstrapping process updates other components that the desired software depends upon. For example, an operating system or DBMS update.

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data_distribution_service_dds is a midware product, and as such, is not generally installed by a user directly, but is integrated into other systems or products. The installer for the desired systems or products (i.e., Wizard or Package) are responsible for installing the correct DDS shared library. In Unix or Linux, a shared object library file is given the extension of .so. In Windows, the shared library is referred to as a Dynamic Link Library with the file extension of ''.dll''. There very few installation or de-installation issues when using DDS.