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These tutorials are about Information Architecture in Web Design.
organizational structure: how the organizational scheme is to be realized in its implementation
Organizational structures define how the information is physically structured for use. It defines the specific relationships between elements. The most common structures are hierarchical, hypertextual, linear, and database oriented. It is also possible to structure information more closely to the scheme it follows. For instance, a geographical scheme could make use of spatial arrangements on the page to provide the organizational structure for the information.
When in doubt, start with hierarchy. Any good information structure is going to have some hierarchical elements to it. The moment you create a main page with links to content pages you have a hierarchy.
A hierarchy is a collection of parent-child relationships. You start with a category. The category has sub-categories, which also may have sub-categories, until you get down to the actual data elements. Hierarchies are ubiquitous. You find them everywhere and they serve to define how we relate to out world. This is because we naturally categorize things. We create associations between things and group them into sets of related items in order to simplify our world. Without our ability to categorize we could not function in the world.
Once you have categorized something, it is only natural to then ask how it is different from other things in the category. In other words, how it fits into the category. This is the process of creating sub-categories, and the construction of a hierarchy has begun.
Hierarchies are not only useful due to their familiarity, but also because they support a top down approach to organizing information. If you work from the top down it becomes much easier to determine what has to be in the information set and what shouldn't be there.
Hierarchies should be both inclusive and exclusive.
inclusive: all information is accounted for
Inclusive means that all information is accounted for within the hierarchy. Obviously you cannot include all possible information, so the challenge is to provide all relevant information so that the data set seems complete.
Exclusive means that all information fits into one and only one category. In reality this is rarely possible, but the best approach is to design you hierarchy as if it were possible and then use other information structures to address the exceptions.
exclusive: everything fits into one and only one category
Hierarchies also have the benefit of allowing for multiple information hierachies accessing the same data. For instance you could look for information in an online store by product type or manfacturer, or even intended use. Or a library can be organized by title, author, subject, and call number.
When working with hierarchies, you should work to balance breadth and depth.
Breadth is how many options, or sub-categories there are on each level. If you menu pages each have a hundred links taking you to specific locations in the site, you can get around really fast if you already know where you are going and how to get there, but if you don't know where you are going you will get lost quickly and give up in frustration.
Depth is how many layers, or menus someone has to click through to get to useful information. The ideal is that you should be able to get anywhere in the site in three clicks or less. If it is taking more than five, you are definitely starting to lose your audience.
Linear information structures are structures that have a sequence to them. They are bested suited for walkthroughs of topics or of sequential listings of groupings of data. A good example of a linear structure is a slide show. Another is an alphabetical listing of books by author.
Wait, didn't I just talk about listing by authors in terms of hierarchy and now I am saying it is linear. Yes. It is actually both, since we use alphabetical listings hierarchically, but they are actually linear. What does that mean?
Well, assume you are going to a library looking for a book by someone named Miller, and it has an old card catalog, so we can't just type his name into a search engine. The card catalog has an alphabetical listing by author, which is a linear structure. Do you start with the first author listed (Aalverson, Aaron) and look through every name until you get to Miller, or do you skip to the M's, and then try to find the Mi's. Most probably the latter. In other words you treat it like a hierarchy. Of course, once you get to Miller, you still have to walk through all the authors named Miller to find the book you are looking for.
The nice thing about linear structures is that they can often be chunked into categories, such as the category of all authors who last name begins with "M".
Hierarchy is good for rapidly working down to specific topics, but there comes a point where there may be some data left to sort through that can't be arranged into any particular hierarchical structure, but do have some sort of sequential arrangement to them. At this level, linear structures are the most useful. They are used when you have to manually sift through the results.
Hypertextual / Networked
Another way of structuring data is the hypertext, or networked model. The hypertext model is used to link together pieces of information that my be related but don't fall cleanly into a given organizational structures. A good examples is the "see also" listing in the yellow pages of a phone book, in the item listings in an encyclopedia. They tell people where else they can look for related information.
Hyperlinked information structures are an excellent supplemental structure, but they aren't much use the the primary information structure. The problem with them is that they are too dependent on the idiosyncracies of the author. They are used to establish relationships between things that are not normally associated with each other, but in the given circumstance have a certain relationship. This means that it is hard for the user to build a mental model of the stucture, since it can appear to be totally random to someone who doesn't understand the relationships being expressed.
Information can also be structured as a database. This may be directly reflected in a navigation system that allows users to search the database directly with a search form, or it may be hidden behind hierarchical or other types of navigation systems.
Database structures are best used for information that can properly be stored in a database. In other words, it should be used as a model when the information is really being stored that way.
Database structures can greatly facilitate searching for specific information, although they can give problems to people who don't know what they are looking for. They are also best suited for information that is all of the same type. Online stores rely heavily on database models since their information is mostly of the type of "saleable products", each with clearly defined characteristics.
Database models do also give us useful tools that are even helpful to apply to other organizational types. Most databases work with a controlled vocabulary, which means that there are a limited number of ways to look for a specific information. Rather than trying to second guess users for every possible variation that describes something, a set of keywords are assigned. If something other than these keywords are used in the search, then all the user gets is a recommendation as to the keywords they may want to be using. If users do not know the keywords, having a limited set of search terms makes it easier to organize a hierachical interface that allows people to search the contents with a point and click method.
Any information structure you should use should make use of a controlled vocabulary. You cannot account for every possibility, but if you pick you descriptive terms carefully you will end up with keywords that people can readily associate with what they are looking for, making their search easier.