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Hub, repeater, switch, router, gateway, bridge

HUB Hub is a controller that controls the traffic on the network.  The following important properties of hub are:  1) It amplify signals. 2) It propagates signals through the network. 3) It does not require filtering. 4) It does not require path determination for switching. 5) It is used as network concentration points. Hubs are basically two types: 1) Active hub 2) Passive hub Active hub: A ctive hub works as repeater which is a hardware device that regenerates the received bit pattern before sending them out . Passive hub : A passive hub is a simple hardware device which provide a simple physical connection between the attached devices. Advantages of hub: It cannot filter the traffic full stop feeling generally refers to a process or device that screens network traffic for certain characteristics such as source address and destination address and protocol. Disadvantages of hub: On a hub, more than one user may try to send data on the netwo...
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Data Warehousing

  Data Warehouse is open to an almost limitless range of definitions. Simply put, data warehouses store and aggregation of a company's data. Data warehouses are an important asset for organisations to maintain efficiency, profitability and competitive advantages, organisations collect data through many sources- online, call centre, sales needs, inventory management. The data collected have degrees values and business relevance. Figure shown below shows the architecture of a typical data warehouse and illustrate the gathering of data, the storage of data, and the quaring and data analysis support. Different steps involved in getting data into a warehouse are called as extract, transform and lode or ELT tasks; extraction refers to getting data from the sources, while loaders reference to loading the data into data warehouse. Characteristics of data warehouse: Multidimensional conceptual view Generic dimensionality Unlimited dimensions and aggregation le...
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Generalization and Specialization

Generalisation is an abstraction for sharing similarities among classes while preserving their differences. For example, each piece of equipment has a manufacturer weight and cost . Pumps also have suction pressure and flow rate. Tank also have volume and pressure we would like to define equipment features just once and then add details for pump, tank and other equipment types. Generalisation is a relationship between a class and one or more refined versions of it. The class being refined is called superclass and each refined version is called a subclass. For example equipment is the superclass of pump and tank. Attributes and operations common to a group of subclasses are attached to the superclass and shared by each subclass. Each subclass is set to inherit the feature of its superclass, for example, pump inherites attributes manufacturer, weight and cost from equipment. Generalisation is sometimes called the "is-a" relationship because each instance of a subclass is ...
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