size pattern

Number, length, count.

Quantity before quality.

A data element with some length or another numeric property.

Data elements with known size can be arranged and compared independent from their actual content. Size is relevant also because processing and storing data is always limited by size.

• Use a special element as end-marker such as the null byte for null-terminated strings (prohibition).
• Explicitly encode size value and content in an embedding.
• Use fixed size elements only.

• The size of a byte is 8 bit.
• All finite data types have limited size.
• Numeric data types represent a size.
• UTF-8 is a variable width encoding that expresses the number of bytes of a character with the number of 1 bits in the first byte.
• The possible number of occurrences of a data element can be expressed in schema languages, for instance with :n-m (BNF), minOccurs/maxOccurrs (XSD), and maxCardinality/minCardinality (OWL).

• The prohibited end-marker may be allowed to be escaped. For instance the ending double quote in a string may be encoded as \". Such encoding requires to parse the full content, contradicting the motivation of the size pattern.
• The conceptual difference between number (multiple elements) and size (one element) is not clear in all data.
• Counting requires to detect boundaries between elements (see sequence and separator patterns).

• Sizes can be constrained by a schema.
• The number of elements in a container is a size.
• The size pattern includes the idea of (natural) numbers. Ordinal numbers in contrast are covered by the sequence pattern.

Knowing the exact size of an element allows to skip its internal structure (atomicity).