• keep related stuff together
• tell you something about what’s inside
  • how related
• help you get at what's inside

• Tuple
• Set
• List
• Array
• Tree

• ("James Frew", 261, "W", 2007)
  • name, course#, quarter, year

• names and types of attributes

Operations

• read/write tuple
• read/write attribute

Associate multiple attributes with a single object

• "I want to know the values of a₁, a₂, ..., a_n for every x"

Manipulate all attributes of an object as a single unit

Examples

• business card
• field measurement
• survey response

• homogeneous: all same type
• e.g.: set of tuples
  • {
    ("James Frew", 261, "W", 2007),
    ("Hunter Lenihan", 260, "W", 2007)
    }

• number and type of elements

Operations

• add/delete element
• intersection/union of two sets

Gather all related objects into a single bag

Lowest-overhead aggregation

• no implied relationship other than same type

• all the business cards you collected at the last conference
• all the measurements you collected on your last field trip
• all the responses to your survey

• e.g.: list of tuples
  • ("James Frew", 261, "W", 2007) →
    ("Hunter Lenihan", 260, "W", 2007)

• number, type, and sequence of elements

Operations

• prepend/append element
• walk (go to next element)
• read/write element

Preserve ordering between objects

• "These otherwise unrelated things happened in this order"

Simple structure

• reference to next element
  or
• delimited sequence

Examples

• text file

NB: list vs set

• list: order is built-in
• set: order may be applied by sorting on attribute values

Ordered, addressable aggregation

• e.g.: array of tuples

...	...
i	("James Frew", 261, "W", 2007)
i+1	("Hunter Lenihan", 260, "W", 2007)
...	...

• number of dimensions
• interleaving of dimensions
• domain of each dimension
• type of element

Operations

• read/write i^th element

Preserve dimensional relationships between objects

• "These things happened at fixed intervals"

Easily updated

• individual elements directly addressable

Examples

• quantized field
  • digital image
  • model output

Hierarchical aggregation

• root
  • leaf
  • node
    • leaf
    • leaf
    • node
      • leaf
    • leaf
  • leaf

• nodes vs leaves

Operations

• descend/ascend
• insert/delete node/leaf
• read/write node/leaf

Preserve hierarchical relationships between objects

• nested containment
• superset/subset
• generalization/refinement

Examples

• filesystem (directories and files)
• XML document
• taxonomy