General Requirements for a Software Distribution Mechanism

Introductory Notes

Software distribution issues are divided into three components here: (1) version control, (2) distribution, and (3) installation. We discuss general requirements and concerns for these three areas, to serve as a starting point for choosing software or recommending techniques for implementing software distribution mechanisms. Another document lists more specific guidelines for developers writing installation scripts. (See Installation Guidelines.)

Original Document Based on the Meeting of 9/19/95

We agreed that version control, distribution, and installation were all separate, but related problems. If we keep them uncoupled we will be in a better position to combine solutions in various ways. (EX: If we agreed on an installation mechanism, we could use several different modes of distribution, such as FTP, WWW, and Mandarin). We really are concerned with Mac and Windows here, and should not worry about Unix for the time being.

DISTRIBUTION

REQUIRED features and capabilities:

• Provide an easy way for users to get new applications (and all associated pieces) and new versions of applications as well as documentation , etc., for all software both internally-developed and commercial.
• Be able to distribute more than one version of the same application, at the same time for exception cases, where installation of the current application would cause other things to break. Supporting the distribution of more than one version of an application will facilitate the distribution of alpha and beta copies as well.
• Be able to restrict distribution to "on Campus" people
• Not force people to upgrade at inconvenient times.
• Make sure that anyone who has a need to distribute software across multiple departments has an easy way to distribute software (not just IS software).

DESIRED features and capabilities:

• Keep as few copies of the binaries as possible (preferably 1), so that they are easily kept in synch, and the "official" binary is easy to identify, even if we provide several transportation mechanisms (Ex: FTP, Techinfo, appleshare...) NOTE: If we don't solve this with a technical solution, then we will require some human resource to do this.

INSTALLER

REQUIRED features and capabilities:

• Make sure there is an easy way to deinstall.
  1. Ability to remove every component installed by previous installation process. (required)
  2. Ability to put back everything changed or erased during previous installation process. (desirable)
  3. Log of all components added, changed, or removed. (required)
• Be able to install more than one version of the same application, at the same time except in cases where installation of multiple copies of the application would cause other things to break.
• Be able to install all parts of the software in the correct places and edit INI files (for example) as needed.
• Support the ability to avoid overwriting existing files such as DLLs without checking versions (or asking the user).
• Behave differently Installer needs to be able to do different things depending on hardware/software status and configuration or questions answered by the user. (Example: Check disk space, operating system level, type of CPU, etc.)

DESIRED features and capabilities:

• Installer should log what it does.
• There should be one installer for each platform, but it need not be the same for all platforms.
• Installation script should be able to clean up after an error.

VERSIONING

REQUIRED features and capabilities:

• Know when a new version is available or when a piece software is out of date.
• Support several states for updatable software, such as required, recommended, and optional.

DESIRED features and capabilities:

• Check version at runtime.
• Check the version of everything on a whole machine.
• Each Component should be able to identify its version.
• Check that everything needed to run an application is available at startup.

MISCELLANEOUS

• We should maintain a database of all applications and their components and dependencies
• We may need to solf the "bootstrap" problem if special software is needed for the distribution mechanism.
• "Mechanisms for license or counting uses, etc., are considered outside of the scope of the software distribution requirements."
• We need some way of checking to make sure that the binaries haven't been tampered with. For now this could be done out-of-band through a cryptographic hash/digest algorithm such as MD5 or SHA. Eventually this function might need to be built into the installer.