Granularity

See also: grain and film grain

Granularity is a measure of the size of the components, or descriptions of components, that make up a system. Granularity is the relative size, scale, level of detail or depth of penetration that characterizes an object or activity. It is the "extent to which a larger entity is subdivided. For example, a yard broken into inches has finer granularity than a yard broken into feet."^[1]

Systems of, or description in terms of, large components are called coarse-grained, and systems of small components are called fine-grained; here coarse and fine are descriptions of the granularity of the system, or the granularity of description of the system.

An example of increasingly fine granularity: a list of nations in the United Nations, a list of all states/provinces in those nations, a list of all counties in those states, etc.

The terms "fine" and "coarse" are used consistently across fields; but the term "granularity" itself is not. For example, in investing, "more granularity" refers to more positions of smaller size, while photographic film that is "more granular" has fewer and larger chemical "grains".

In physics

A fine-grained description of a system is a detailed, low-level model of it. A coarse-grained description is a model where some of this fine detail has been smoothed over or averaged out. The replacement of a fine-grained description with a lower-resolution coarse-grained model is called coarse graining. (See for example the view of the second law of thermodynamics in the article Maximum entropy thermodynamics)

In molecular dynamics

In molecular dynamics, coarse graining consists in replacing an atomistic description of a biological molecule with a lower-resolution coarse-grained model that averages or smooths away fine details. Coarse-grained models have been developed for investigating the longer time- and length-scale dynamics that are critical to many biological processes, such as lipid membranes and proteins.

In computing

In parallel computing, granularity means the amount of computation in relation to communication, i.e., the ratio of computation to the amount of communication.

Fine-grained parallelism means individual tasks are relatively small in terms of code size and execution time. The data are transferred among processors frequently in amounts of one or a few memory words. Coarse-grained is the opposite: data are communicated infrequently, after larger amounts of computation.

The smaller the granularity, the greater the potential for parallelism and hence speed-up, but the greater the overheads of synchronization and communication. (The last two paragraphs are copied verbatim from FOLDOC.)

In Reconfigurable Computing and Supercomputing

In Reconfigurable Computing and in Supercomputing these terms refer to the data path width. The use of about one bit wide processing elements like the configurable logic blocks (CLBs) in an FPGA is called Fine-grained computing or Fine-grained reconfigurability, whereas using wide data paths, such as, for instance 32 bits wide resources, like microprocessor CPUs or data-stream-driven data path units (DPUs) like in a reconfigurable datapath array (rDPA) is called Coarse-grained computing Coarse-grained reconfigurability.

Data Granularity

The granularity of data refers to the fineness with which data fields are sub-divided. For example, a postal address can be recorded, with low granularity, as one field:

address = 200 2nd Ave. South #358, St. Petersburg, FL 33701-4313 USA

or with high granularity, as many fields:

street address = 200 2nd Ave. South #358
city = St. Petersburg
postal code = FL 33701-4313
country = USA

or even higher granularity:

street number = 200
street = 2nd Ave. South #358
city = St. Petersburg
postal code state = FL
postal-code-first-part = 33701
postal-code-second-part = 4313
country = USA

Higher granularity has overheads for data input and storage, but offers benefits in flexibility of data processing.

In credit portfolio risk management

In credit portfolio risk modeling, granularity refers to the number of the exposures in the portfolio. The higher the granularity, the more positions are in a credit portfolio, providing a higher degree of size diversification, which in turn reduces concentration risk. This is colloquially known as "not putting all your eggs in one basket".

In photographic film

In photography, granularity is a measure of film grain. It is measured using a particular standard procedure but in general a larger number means the grains of silver are larger and there are fewer grains in a given area.

In business

The concept of granularity is starting to be used also in domains other than physics. For example, in business it has been written about in the book, The Granularity of Growth: Making choices that drive enduring company performance. Its authors (Viguerie, Smit, and Baghai) say that there’s a problem with the broad-brush way that many companies describe their business opportunities. They argue that real opportunities for company growth can emerge only from a much finer understanding of market segments, their needs, and the capabilities required to serve them well than is typically done. According to the authors, to uncover these small “pockets of opportunity,” executives need to dig down to a deeper level of their organization, which in large companies introduces the challenge of making broad choices at a refined “granular level” without losing focus.

General examples

At a September 2006 White House press briefing, presidential press secretary Tony Snow responded to a question about an asserted link that had existed between Saddam Hussein and al Qaeda terrorist Abu Musab al-Zarqawi. Snow said that Bush indicated there was "no operational relationship" between Zarqawi and Saddam but added, "we just don’t have that kind of granularity in terms of the relationship. And, therefore, we’re not going to outrun the facts."^[2]