Federated Database
Federated database refers to a variety of data sources in order to manage a single individual, but also to maintain the autonomy of the various data sources and integrity, when a user access to dispersed data source, just as easy as operating a single database.
If the eighth edition of IBM database software DB2, which adopts the Federated Database Technology, emphasized that programmers need not use other applications, you can directly access, analyze and integrate the various network service environment information; or to enterprise systems search and access to different data library technologies, in order to form a Federated Database.
Federated Database is different from the concept of distributed databases and data warehousing. Distributed database refer to the same types of information, organizational management, the federal database, however, the concept of inter scattered outside, but also includes the integration of heterogeneous data.
In addition, the Federal-style management structure, the various sources of information like a different "Member States" has the independence, whether it is updating, maintenance, and have their own, and do not increase the "central" side burden. When you need to query and access to information, the local side will also give directions, the required information can be returned from various sources in order to ensure real-time updates of information.
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Fiber
The short fiber is optical fiber is determined by the glass material (SiO2) formed a kind of snag optical transmission media, their main principle is the use of light transmission through a high refractive index (Index of Refraction) media, higher than the critical angle (Critical Angle ) point of view into the low refractive index medium will have the principle of total internal reflection, allowing light in this medium to maintain the waveform characteristics of the original transmission.
Basic structure of an optical fiber, such as drawings can be divided into three parts, namely:
1. The core of (Core): a high refractive index of the core of a fiber (Core), namely, fiber optical signal transmission part, core diameter is usually 5 ~ 50μm.
2. Shell part (Cladding): cladding diameter of typically 125μm, coating the outer part of the core, in order to transmit light in the core, the core part of the refractive index of the refractive index than the crust to be large, in order to create full - reflex.
3. Protection layer (Jacket): protection of the surrounding shell to prevent damage to the shell and core optical fiber, usually in the outer cladding layer of a thin coating layer of coating, coating layer material is typically epoxy resin or silicone rubber, mainly to increase the fiber strength. Outside is a set of plastic coating layer, the main material for nylon or polyethylene, but also to increase the fiber strength. If the material points, the most commonly used quartz glass optical fiber, transmission loss due to the smallest, most suitable for use as high-capacity, long-distance transmission of the remaining material of the fiber is greater use of industrial monitoring, short-range transmission, laser medical and Lighting applications.
If the transmission mode for hours, can be divided into single-mode and multi-mode two broad categories, such as photos II:
1. Single-mode optical fiber: its core diameter size limit of about 10μm, only allowing a single mode of light waves in the core of a fiber transmission. Because of its smaller core diameter, low-loss signal transmission, is more commonly used for long-distance transmission, such as submarine cables, telecommunications, and so on the main trunk.
2. Multi-mode fiber: its core diameter between about 50 ~ 75μm, providing multiple paths for a variety of light wave transmission, the light waves at the core of a fiber several kinds of transmission modes simultaneously. Because of different paths have different propagation distance, resulting in a high loss of transmission signal. Terminal equipment, but the lower price for the short-distance communication Guchang.
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