Complete Installation Guide for Oblivion/Part 2/OBMM/Analyze Mod and Package Structure
Analyze Mod and Package Structure
All of the mods used explicitly in this guide are OMOD-Ready, are OMODs, have simple installs or have OMOD Conversion Data (with installation scripts) available; therefore, many details of mod structure and packaging are "invisible" to the user. Many of the specifics are largely only relevant to modders, but mod users need to have a certain basic understanding of these topics as well, especially since it is likely that many mods you will download will not be in any of the aforementioned formats.
...not including OBSE plugins...
Mods may have two parts, plugins and data files. Some have only one or the other. Those that include only data files are what are referred to as "replacers", mods intended to change visual or aural features of the game (or even certain mods.) Data files are merely loaded and used according to rules defined in plugins. As such, no record of which data files are installed for Oblivion is kept for the game, and replacer's files can be switched out at anytime without affecting save files at all. The only minor exception is when dealing with BSAs, if they are registered in the Oblivion.ini, removing them without updating the game's INI, will likely result in the game being unable to fully load. Removing the original BSAs is slightly more tedious than dealing with mod-added BSAs and should generally be left alone.
Plugins are the files that really change how the game is structured (up to a certain level.) A poorly structured plugin can cause crashes and all sorts of issues, but, fortunately, their being causers of serious issues is not the norm. There are two types of plugins, ESMs and ESPs. The former are almost always only resource files, their primary purpose being to hold new records. Mods' ESPs do all of the work, from placing structures to modifying NPCs' inventories. Most mods are simple, and will only have a single plugin, but many have multiple plugins.
ReadMes, with respect to mods' structure, become very important when a mod has multiple installation configurations, not just multiple plugins; although, some complex mods may only have plugins. For example, many mods provide both Vanilla and Shivering Isles (SI) versions of their main plugin. Some mods include an SI add-on plugin, but that is not always a convenient option. Another common example is a mod that provides a full and a reduced version of the main plugin, the latter being stripped of some of the default features (i.e., Ren's Beauty Pack's hairs-only plugin versus the Ren's Beauty Pack Full plugin.) The best way to determine whether or not a mod includes a multiple configuration is to read the installation section of the ReadMe. Furthermore, when choosing add-ons, some may have extra requirements or may not be compatible with other offer add-ons (which might be because there are multiple versions of an add-on.) A complex mod may even have multiple data file configurations, as is the case with cosmetic compilations that may offer various textures for a given body type.
In the end, only one configuration of a mod should be installed. If multiple versions of a plugin are present, any number of problems may evidence themselves in the game. With the exception of INI files and BSAs, if data files (i.e., meshes, textures, voice files, etc.) are not installed to one of the default folders (i.e., Meshes, Textures, Music, Sound, Voice, Font, DLOD, Menus, Video, etc.) they are not installed. If plugins are not in the Data folder (not any subfolders) they are not installed.
Mod downloads are generally of only a few formats: compressed archives (7z, RAR, ZIP, OMOD), executables (EXE) or, in rare cases, loose files (e.g., ESM, ESP, BSA, etc.) The process for dealing with the latter two groups varies greatly, but most downloads will be of one of the types in the former group. For the most part, loose files (so long as they are not pure resource files) can be packed into an OMOD with the 'Add file' function. EXEs are mainly used for quest mods, due to their size. This is good because most quest mods have a simple install structure, and the files installed by such EXEs can simply be packed into a single OMOD via 'Add file'.
Ignoring OBSE plugins (which are a whole different type of extension for the game) mods can have two parts. Compressed archive mod downloads either have a simple package format or a complex format. Simple packages' contents reflect installed mod structure. Once extracted (from the proper location) all files are installed. However, that does not mean that it would be installed correctly. A package that contains only plugins may have multiple versions of some plugins, which the user should choose between instead of installing them all. The installation can be complex, even if the package is not.
Unless you find that you have to repackage a mod's archive, the most convenient way for an OMOD user to analyze a package's structure is via the OMOD creation window. The window itself has to views, Plugins and Data files. The plugin view is the default, and when you add an archive, those are the files you will see listed in the files frame in the bottom half of the window. If you click on the radio button for 'Data files', data files will be displayed (if the archive contains any.) As mentioned earlier, OMOD-Ready downloads and OMODs may have any number of structures, but in order for other types of downloads to be install-ready, the analysis of the archive should evidence an installed mod's structure. Plugins should appear in the frame as "<some plugin>" or "Data/<some plugin>", not "<random folder>/<some plugin>".
When a mod download is neither OMOD-ready nor simple, if it is simple enough (i.e., only a few plugins to choose between) you can use 'edit script' to add a simple OMOD script to take care of the config choices, or, install the OMOD and delete the unneeded plugins afterward. Otherwise, if the mod is some sort of cosmetic mod or texture replacer with lots of custom folders, you may want to install the mod manually (and/or request for someone to create OMOD conversion data for the mod.) For downloads without OMOD conversion data, always check the archive structure before packing it into an OMOD. >> Note: See OMOD Scripts and Script Templates for a few simple examples and links to some helpful scripting resources.
A very popular mod that has extremely odd packaging is Ren's Beauty Pack (v1.1). Many users install it improperly because they figure out that the hair data files for the full one are in the hairs-only archive, but then they also install the plugin that is in that archive, when they should have only installed the data files. The way to repackagee Ren's mod is to unzip the outer archive, and then add both of the contained archives to an OMOD. After filling out the necessary info, a script could be added (via 'Edit script') to ensure that only one plugin is installed (i.e., the script for Ren's mod the OMOD Scripts and Script Templates page). Most mods do not have compressed archives within compressed archives, but the contained folder structure may not be anywhere near install-ready.
Oblivion Script Extender
Bethesda Softworks Archive