Types of Structure Outliners take advantage of what may be the most primitive of relationships, probably the first one you learned as an infant: in. Things can be in or contained by other things; alternatively, things can be superior to other things in a pecking order. Whatever the cognitive mechanics, trees/hierarchies are a preferred way of structuring things. But it is not the only way. Computer users also encounter: links, relationships, attributes, spatial/tabular arrangements, and metaphoric content. Links are what we know from the Web, but they can be so much more. The simplest ones are a sort of ad hoc spaghetti connecting pieces of text to text containers (like Web pages), but we will see many interesting kinds that have names, programs attached, and even work two-way. Relationships are what databases do, most easily imagined as “is-a” statements which are simple types of rules: Ted is a supervisor, supervisors are employees, all employees have employee numbers. Attributes are adjectives or tags that help characterize or locate things. Finder labels and playlists are good examples of these. Spatial/tabular arrangements are obvious: the very existence of the personal computer sprang from the power of the spreadsheet. Metaphors are a complex and powerful technique of inheriting structure from something familiar. The Mac desktop is a good example. Photoshop is another, where all the common tools had a darkroom tool or technique as their predecessor.