etcetera pattern

Ellipsis, partial collection, explicit abbreviating.

Indicate that a collection of data elements is incomplete.

A container or embedding of elements.

Collections may be too large to be expressed, or parts of a collection may be unimportant or already implied by context. This pattern allows for abbreviating and to show that a collection contains more then explicitly expressed.

First, one needs to decide which parts to omit:

• Only express the first or the most important parts.
• Only express mandatory parts and omit the rest (optionality).
• Give a random sample of of elements (garbage).

Second, the etcetera indicator can be expressed in several ways:

• Use a special element as etcetera indicator. This element must be a prohibition to not be confused with normal parts.
• Use obviously wrong elements as placeholders (garbage).
• Define a fixed cut, for instance a maximum length.

• ... or et al. to indicate an abbreviated sequence.
• e.g. to indicate that the included elements are examples from a larger set.
• Omission of parts in the middle of an element with [...].
• Library cataloging rules exist to only include three authors in a record, so the list of authors is always abbreviated if there are more then three authors.

Omission of details can also be an example of generalization and abstraction (see encoding) instead of abbreviation.

• Type and number of omitted parts and the reason for abbreviating are often unclear.
• An etcetera indicator and normal parts of a collection must not be confused (for instance strings that actually end with ...).
• Indicators could also be used to tell that a collection may be extended or that an element can be repeated (see container and schema patterns).

With a fixed cut this pattern also uses the void pattern instead of an explicit etcetera indicator. The void pattern is also similar because it indicates elements. The etcetera pattern in contrast indicates the existence of more elements.

The etcetera indicator only makes sense as part of an embedding (typically a container or sequence).