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Granular Computing: Practices, Theories, and Future Directions

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Encyclopedia of Complexity and Systems Science

Definition of the Subject

Granular Computing (GrC) is still in its inception stage, we use motivation as its statements of importance.

How Important is Granular Computing?

Granulation seems to be a natural methodology deeply rooted in human thinking. Many daily “things” are routinely granulated into sub“things”; for example, the human body has been granulated into the head, neck, and so forth. The notion is intrinsically fuzzy, vague, and imprecise. Formalization is difficult, mathematicians idealized/simplified it into the notion of partitions (= equivalence relations), and have developed it into a fundamental part of mathematics, for example, congruence in Euclidean geometry, quotient structures (groups, rings, etc) in algebra, the concept of “a. e.” (almost every where) in analysis. Nevertheless, the notion of partitions (see glossary), which absolutely does not permit any overlapping among its granules, seems to be too restrictive for real world problems. Even in natural science,...

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Abbreviations

Glossary:

All terms are explained in classical sets, but implicitly, we are assuming all terms and assertions do include fuzzified versions (if fuzzifiable).

Granulation:

Granulation is an operation or a process of forming granules, with a granule being a collection of objects (points) that are drawn together by some constraints, such as indistinguishability, similarity or functionality.

Granular structure:

Granular structure is the collection of granules, in which the internal structure of each granule is visible as a sub‐structure. Informally speaking, granular structure is a collection of white box granules.

Quotient structure:

A quotient structure is the mathematical structure of the collection of granules, in which each granule is regarded as an element (point) of a set, but the interactions among granules are preserved. Informally speaking, a quotient structure is a collection of black box granules.

The collection of \( \{\ldots,-2, 0, 2,\ldots\} \) and \( \{\ldots,-3, 1, 3,\ldots\} \) is a granular structure. Let E be the first subset (even integers) and O be the second subset (the odd integers). We write the two subsets by [E] and [O], when we think of them as points. Then the collection of [E] and [O] (as points) is the quotient structure.

Neighborhood system (local granular model abb. local GrC model):

A domain of interests ( a classical set) U is called the universe. To each point p in the universe, a family of subsets is assigned. Such a family (could be empty) and each such subset is called a neighborhood system \( { \text{NS}(p) } \) at p and a neighborhood at p, respectively. The collection β of such a family at every point of the universe is called a neighborhood system \( { \text{NS}(U) } \) of the universe. Neighborhood and neighborhood system are pre-GrC language; in granular computing, they are called granule and the granular structure, respectively. The pair (\( { U, \beta } \)) is called a local granular model, since each granule is associated with some points.

Topological neighborhood system:

A neighborhood system is called a topological neighborhood system, if it satisfies the axioms of topology.

Binary neighborhood system (binary granular model; binary GrC model):

A binary neighborhood system is a neighborhood system defined by a binary relation R. A (right) neighborhood is defined as follows: \( B(p)=\{x \mid(p,x)\in R\} \). The collection B of B(p) at each p is the (right) binary neighborhood system. Similarly, we can define a left version: A left neighborhood system L is defined by the \( L(p)=\{x \mid(x, p)\in R\} \) at every point p. Note that the right and left neighborhood systems determine each other. The pair (\( { U, \beta } \)) is called a binary granular model, where β is right (left) neighborhood system or R.

pre‐Topology:

Pre‐topology is a general term referring to the neighborhood system, which includes the topological neighborhood system and binary neighborhood system as special cases. Technically, it is equivalent to the neighborhood system.

Bag:

A bag is similar to a set, but allows an element to appear more than once. For example \( { \{1, 2, 1, 2, 1\} } \) is a bag, but not a set. If a bag contains n elements, we may say it is an n‑bag. For example, the previous bag is a 5‑bag.

Relational structure (relational granular model; rela-tional GrC model):

A family of classical sets is called a universe and denoted by \( { \mathcal{U} } \). A Cartesian product of an n‑bag of \( { \mathcal{U} } \) is called an n‑product set. A n‑ary relation is a subset of an n‑product set. A collection β of n‑ary relations (n could vary) is called a relational structure. The pair (\( { U, \beta } \)) is called a Relational GrC Model. Note that this relational structure, except the size, is similar to the relational structure (without functions) of the First Order Logic; the Relational GrC Model permits n to be any cardinal number.

Partial covering (global granular model; global GrC model):

Let U be a classical set, called the universe. Let \( { \beta =\{F^1, F^2, \ldots \} } \) be a family of subsets. Such a β is a partial covering, and (full)covering, if the union of β is the whole universe. The pair (\( { U, \beta } \)) is called a Global Granular Model (Global GrC Model).

Equivalence Relation:

A binary relation \( { \mathcal{R} } \) is called an equivalence relation, if it has the following properties: Let u, v, and w be elements of U.

reflexive::

\( { u \mathcal{R} u } \)

symmetric::

\( { u \mathcal{R} v } \) implies \( { v \mathcal{R} u } \)

transitive::

\( { u \mathcal{R} v } \) and \( { u \mathcal{R} w } \) implies \( { u \mathcal{R} w } \)

reflexive::

\( { u \mathcal{R} u } \)

symmetric::

\( { u \mathcal{R} v } \) implies \( { v \mathcal{R} u } \)

transitive::

\( { u \mathcal{R} v } \) and \( { u \mathcal{R} w } \) implies \( { u \mathcal{R} w } \)

Partition:

A partition \( { \mathcal{P} } \) of a classical set U is a collection of subsets that are mutually disjoint and their union is U. Each subset is called an equivalence class. This name is derived from the fact that partition is equivalent to the following equivalence relation: We define \( { u \mathcal{R} v } \), if and only if u and v belong to the same equivalence class. Such \( { \mathcal{R} } \) is the equivalence relation corresponding to the partition \( { \mathcal{P} } \). Note that a partition is a special type of a granular structure, so an equivalence class is a special granule.

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Lin, T. (2009). Granular Computing: Practices, Theories, and Future Directions. In: Meyers, R. (eds) Encyclopedia of Complexity and Systems Science. Springer, New York, NY. https://doi.org/10.1007/978-0-387-30440-3_256

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