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This OEP refers to Octave's design of the pkg system. The purpose of this system is to handle the installation, loading, and removal of Octave packages.

The current implementation of pkg has problems mainly when there's both local and global installations of packages, and when multiple octave and package versions try to coexist. This document attempts to design a solution for this.

The main idea of the solution is to keep database files with each package location and dependencies, and allow for the merge of such files.

To allow reinstallation of the packages, we propose to keep the source of the package. This would also make it easier to run the tests of packages.

Rationale and examples

This design is meant to allow the following:

 * keeping multiple versions of the same package installed and load a specific one
 * keep packages installed for multiple versions of Octave, specially in the case of
   .oct files which need to be rebuilt for each octave function
 * reinstall a package from its cache after installing new octave version
 * run the tests from packages (find tests in .cc sources)
 * clean the package cache
 * usage of alternate database files
 * usage of packages in remote directories which may not be available at all

Case 1

Denise installs Octave 3.4.3 and installs the latest version of the financial (1.0.4) and image (2.0.0) package with "pkg install -forge financial image". After installing the packages, pkg keeps the tarballs in the system in cache for future use. The financial package is comprised of only .m function files while the image package is a mixture of .m and .oct. After installation, she runs `pkg test financial test` which runs all tests in the package (using the cached package to run the tests in the .cc files).

Later, Denise installs Octave 3.6.2 but keeps the previous version of Octave on the system since some of her old code no longer runs correctly. Loading the financial package is no problem but loading the image package returns the error

 pkg: image package not built for current version of Octave. Run `pkg reinstall image`

Denise runs `pkg reinstall image` which reinstalls the package (effectively keeping the .m files, but simply rebuilding the oct files for the new version). Depending on the Octave version she will run. Different paths will be loaded even though the package is the same.

A new version of the financial package (1.2.0) is released which is dependent on Octave 3.6.0. While using Octave 3.6.2, Denise installs the new version of the package "pkg install -forge financial". The files for the previous version of the package are kept altough "pkg load financial" will only load the latest version. However, when Denise is using Octave 3.4.3, as financial 1.2.0 requires Octave 3.6.0, pkg load will only load financial 1.0.4.

Case 2

Owen is stuck using the financial package 1.0.4 because some of his code no longer works in the latest versions. However the latest version of financial is 1.2.0 and pkg install -forge would install that version instead. He installs the old version of the package with "pkg install -forge financial-1.0.4".

But Owen wants to fix his code for the new version so also installs the new version of the package to experiment. On his code, he then uses "pkg load financial-1.0.4" while "pkg load financial" always loads the latest version of the package.

Case 3

Lisa is using Octave in a remote machine on the biochemistry department. The system administrator installed Octave 3.6.2, signal package 1.2.0, and general 1.0.0. Lisas uses all of them but she also requires the image package. However, the system administrator does not have time to access security issues with the package and tells her to install that package locally. She runs "pkg install -forge image" which installs the package in her home directory. When she runs "pkg list" she sees both the global packages and her own packages

When Octave 3.6.3 is released, Lisa wants to use the new version since it fixes one bug that has been aanoying her for a long time but the system administrator does not want to make the update and tells her to build it herself locally

Case 4

Diana is a student that wants to run her code in the departmental cluster. However, the system does not have an installation of Octave and she needs to install it on her home directory. When she installs packages, these installations are global (to her home directory) since she has write permissions on the directory where octave is installed. She installs the signal and image package.

Ligia is a colleague of Diana that wants to use the same cluster but wants to save herself from the trouble of building Octave. So she uses Diana's install of Octave. Since all packages were installed globally, Lígia has no trouble using the same packages. However, Lígia also needs to use the struct package and installs it "pkg install -forge struct". Since she does not have permissions to write on Diana's home directory, her install of the struct package is local. When Diana runs Octave she does not see the struct package installed, it only shows up for Ligia.

Diana wants to use the same version of the struct package that Ligia already installed but that package was installed locally to Ligia's home directory. She uses "pkg load-list /home/ligia/.octave/packages.db" to add the list of ligias packages to her own list of available packages. which she can load.

Case 5

John is a professor of biomechanics and uses Octave on his classes. Most of the exercises he gives to the class require the use of multiple packages in Octave Forge. Depending on the class, the requires packages are different. He creates a metapackage for his student listing all required packages. The students install it with "pkg install -url path-to-his-metapackage". The metapackage has no file it simply lists a bunch of package has dependencies. Since pkg solves this dependencies automatically, a message showing which packages will be installed is displayed before doing it.

Where to install things

These should not be hardcoded and taken from octave_config_info. There's many paths there whose purpose is explained on octave sources buil-aux/common.mk (see the Where To Install Things and Octave-specific directories sections on that file.)