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MCA Articles
Page 94 of 95
Comparison between E-R Model and Object Oriented Model
The detailed comparison on the E- R model and Object Oriented Model is given as follows −E-R ModelER model is used to represent real life scenarios as entities. The properties of these entities are their attributes in the ER diagram and their connections are shown in the form of relationships. An ER model is generally considered as a top down approach in data designing.An example of ER model is −Advantages of E - R modelThe data requirements are easily understandable using an E - R model as it utilises clear diagrams.The E-R model can be easily converted into a relational database.The ...
Read MoreRepresentation of class hierarchy in DBMS
Class hierarchy can be viewed one of two waysSpecialization (Top Down Approach)Generalization (Bottom Up Approach)SpecializationSpecialization is a process of identifying subsets of an entity that shares different characteristics. It breaks an entity into multiple entities from higher level (super class) to lower level (subclass). The class vehicle can be specialized into Car, Truck and Motorcycle ( Top Down Approach)Hence, vehicle is the superclass and Car, Truck, Motorcycle are subclasses. All three of these inherit attributes from vehicle. Moreover, these three share those attributes among themselves while containing some other attributes which make them different.GeneralizationGeneralization is a process of generalizing an entity which ...
Read MoreMoving Object Databases
Moving objects are those whose position changes frequently over a period of time. Conventional databases don't know how to handle this scenario, as they assume the data objects are stationaryIn this case, we use moving object databases. These databases can store information about moving objects and allow querying on them.For example- The location of nearest taxis for a particular customer can be found using querying on moving object databases.The approaches used in handling moving object databases are:Location ManagementThe current locations of the objects are saved in the database and estimations are made on their near future positions. This information is ...
Read MoreMandatory and optional Participation
Mandatory and optional participation are observed in E-R models between 2 different entities.Mandatory ParticipationIn the mandatory participation, for every instance of entity A, there must exist an instance of entity B and vice versa.An example of Mandatory participation would be relationship between mother and child. The child entity would exist only if there were a mother and similarly a mother would exist only if there were a childOptional participationIn optional participation, it is not necessary for all the instances of the entity to participate in a relationship. It may be that the number of instances participating for a particular entity ...
Read MoreDifference between Synthesized and Inherited Attributes
Both Synthesized and Inherited Attribute are the part of semantics of a language that provide meaning to its constructs, like tokens and syntax structure. Semantics help interpret symbols, their types, and their relations with each other and its analysis judges whether the syntax structure constructed in the source program derives any meaning or not. Now on the basis of features of attributes we can distinguish between Synthesized and Inherited AttributesFollowing are the important differences between Synthesized and Inherited Attributes.Sr. No.KeySynthesized AttributeInherited Attribute1DefinitionSynthesized attribute is an attribute whose parse tree node value is determined by the attribute value at child nodes.To ...
Read MoreFrame Structure for OFDMA with Time Division Duplexing
Orthogonal frequency division multiple access (OFDMA) is a multi-user version of digital data modulation scheme OFDM (orthogonal frequency division multiplexing). In OFDM, a single stream of data is divided into several separate sub-streams for transmission via multiple channels. OFDM uses the principle of frequency division multiplexing (FDM), where the available bandwidth is divided into a set of sub-streams having separate frequency bands.In OFDMA, multiple access is achieved by assignment of different subsets of subcarriers to individual stations. This permits transmission to go on simultaneously at lower data rate from several stations.The stations assigned to a given subcarrier alternate between sending ...
Read MoreThe 802.16 Physical Layer
The IEEE 802.16 is a set of standards that lays down the specifications for wireless broadband technology. It has been commercialized as Worldwide Interoperability for Microwave Access (WiMAX) that is responsible for delivery of last mile wireless broadband access. It lays down the standards for both physical layer as well as medium access control (MAC) layer for WiMAX.Physical Layer Features of WiMAXThere are two popular services of the physical layer −Fixed WiMAX.Mobile WiMAX.WiMAX initially provided data rates of 30 – 40 Mbps. The updated version that came in 2011 provides up to 1 Gbps data rates for fixed stations.It operates ...
Read MoreThe 802.16 Architecture and Protocol Stack
The 802.16 is a set of standards defined by IEEE (Institute of Electrical and Electronics Engineers) that lays down the specifications for wireless broadband technology. It has been commercialized as Worldwide Interoperability for Microwave Access (WiMAX) that is responsible for delivery of last mile wireless broadband access.The IEEE 802.16 lays down the standards for both physical layer as well as medium access control (MAC) layer for WiMAX. It initially provided data rates of 30 – 40 Mbps. The updated version that came in 2011 provides up to 1 Gbps data rates for fixed stations. It operates in the frequency band ...
Read MoreOrthogonal Frequency Division Multiplexing (OFDM)
In data communications and networking, orthogonal frequency-division multiplexing (OFDM) is a method of digital data modulation, whereby a single stream of data is divided into several separate sub-streams for transmission via multiple channels.OFDM uses the principle of frequency division multiplexing (FDM), where the available bandwidth is divided into a set of sub-streams having separate frequency bands. OFDM was introduced in 1966 by Chang at Bell Labs and was improved by Weinstein and Ebert in 1971.Working Principle of OFDMOFDM is a specialised FDM having the constraint that the sub-streams in which the main signal is divided, are orthogonal to each other. ...
Read MoreAsymptotic Complexity
Asymptotic AnalysisUsing asymptotic analysis, we can get an idea about the performance of the algorithm based on the input size. We should not calculate the exact running time, but we should find the relation between the running time and the input size. We should follow the running time when the size of input is increased.For the space complexity, our goal is to get the relation or function that how much space in the main memory is occupied to complete the algorithm.Asymptotic BehaviorFor a function f(n) the asymptotic behavior is the growth of f(n) as n gets large. Small input values ...
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