SharePoint Server 2010 offers metadata and content types that are used to create information architecture, along with several other pieces. There are new features that include managing metadata, term sets, and metadata navigation for the metadata. This is true even when the information has to be retrieved. Various operations allow for the modification of content types including columns. They can be blocked on large lists that will be important for planning.
If you want to use metadata navigation and other retrieval methods you can benefit from the metadata content. Your plan should include these types of columns when you are in the design phase. The larger list of scenarios for the metadata though won’t be useful. Yet is a required element for users so that they can access the system. A possibility is that there will be items you need to find and only search will help you to access them.
There are three ways in which the metadata can be applied, Built into the system processing, custom configurations & code, and manual application by users. If you want to be able to use columns when you retrieve content then the items should have a value that is specified for the column. This allows the plan for navigation to be concrete. It also allows for the metadata to be filled in. The method of guaranteeing the correct metadata is applied through a built in process as well as some customizations. The goal is for the user to have to do less work.
With metadata selectivity there is the important issue of the size of the list as it is going to get bigger. There are recommendations that apply based on the size of the list, but they aren’t so vital when you are talking about lists that are small in size. Selectivity refers to the number of items that have to be considered for the return results of a query. There are two things to consider here actual selectivity and throttling selectivity.
With actual selectivity you are looking at the total number of results that match a given query search. With throttling selectivity you are looking at the number of results that have to be considered after you apply all the conditions. Most of the time actual selectivity is what will be looked at. Throttle selectivity is mainly used to impact the use of the SQL Server.
In order to use the metadata navigation correctly as well as other filtering options the metadata has to be selective. The list views that are part of the default should show thirty items for users to can results. If there are more than thirty results then it is hard to find what is relevant. As you get more and more results it is harder to find what you are really looking for. Selectivity helps to reduce the chance of operations exceeding the list view threshold.