High Cohesion Principle

High Cohesion Principle Responsibilities of a module should be highly related and focused so that the module has only one reason to change. 

There are four fundamental and yet important software design principles—low coupling, high cohesion, open for extension, and closed for changes. We can simply call them high-low open-closed principles. 

Please note that layers and tiers are two different concepts. Tiers mean the physical separation of subsystems—each subsystem runs on a different hardware or the same hardware but in different processes. In a multitiered system, the interaction between the subsystems is accomplished through remote procedure calls (RPCs). Any RPC involves network overhead and therefore has a performance penalty whether the remote procedure is on a separate hardware or on the same physical hardware but in a different process. Layers, on the other hand, are logical separations of the subsystems. Each layer can run on a different physical tier, or all layers can run on a single tier. The purpose of physical tiers is to leverage distributed hardware resources or to reuse a piece of software that is deployed on a different hardware that your system wants to leverage. The purpose of layered software architecture is to separate the system into highly cohesive and loosely coupled modules (see Chapter 2 for software development principles). 

In principle, oxygen may occupy interstitial or substitutional sites in the crystal, but mostly due to the high cohesive energy of the late TMs, the latter... 

Ever since this breakthrough, C60 has been intensively studied and has shown its rich bonding characteristics in various environments, from van der Waals cohesion to ionic and metallic cohesions, and even to the extent of covalent bonding, together also with its rich electronic properties including high transition-temperature (Tc) superconductivity in alkali-doped C60 fullerides. This article reviews the first-principles quantum-mechanical studies of these electronic and bonding properties of C60. 

This test method is preferably used for the comparative evaluation of adhesives and surface pretreatment methods, since it enables the indication of the differences in the adhesive and cohesive behavior of the adhesive layers with high sensitivity. Pressure-sensitive adhesives (adhesive tapes, adhesive labels) are also tested according to this principle. 

The success of simulation is evident The first-principle approach enables one to predict with a high accuracy the strength of interatomic bonding for metals with different electronic structures. The cohesive energy of metals varies from —0.94 eV/atom (0.905 kj/mol) for potassium to —6.82 eV/atom (656.76 kj/mol) for molybdenum and —8.90eV/atom (857.07 kJ/mol) for tungsten. 

Ten years ago interest centered in the structural principle governing the high polymers, the forces of cohesion of the large molecules and the paths leading from the chemistry of the low molecular substances to the high polymers. Today these fundamentals may be regarded as solved in essentials and the research worker in this field is occupied with other questions. 

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