Data model and Relational Database Model

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A data model

               The data model is used to represent real facts of the application. An application may contain many facts however one has to focus only on important facts ignoring the others. For example in case of student details application, student name, roll no, address have to be described however student may also contain other facts like fathers name etc. which may not be relevant.  Some of the salient features that model must may have are listed.
  • Data model mainly describes the data, which gets stored and processed in a given situation.
  • A data model may describe data and various levels and description may be at logical / physical levels or from the point of user.
  • A data model proposes a set of concepts for description of the nature of data and inter-relationships between them along with the syntax.
  • A model should have as minimum concepts, which are close to real world so that user can understand the model and verify.
  • The model should provide primitives by which meaning of data can be captured. The meaning contains type of value data items take their inter-relation to higher level entities and the correctness requirement for them.

Relational Database Model

             Insertion anomalies and redundant data are problems associated with an early database model known as a hierarchical table (parent-child table). Network database (owner-member table) models were problematic as well. These two models led to the development of the relational database model.

The relational model for database management is a database model based on first –order predicate logic (mathematical theories applied by Dr. E. F. Codd). A database model organized in terms of relational model is a relational database model (RDM).

In a RDM, data are stored in a relation or table (those terms may be used interchangeably.) Each table contains rows or records, (also called tuples), and columns which represent attributes or fields. Each record or row is represented by a unique field known as the Primary key. The categories of relationships in a RDM are one-to-one, one-to-many, and many-to-many. A many-to-many relationship must be broken down into numerous one-to-many relationships. If a pair of tables share a relationship, data can be retrieved based on matching values of a shared field between the tables. Data is retrieved by specifying fields and tables using a standard query language known as Structured Query Language (SQL). Most DBMSs (Database Managements Systems) use SQL to build, modify, maintain and manipulate databases. Thorough knowledge of SQL isn’t always necessary since most DMBSs use a graphical interface to generate SQL statements and retrieve data. It is good, however, to have basic knowledge of SQL.

Database Management System (DBMS)

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Data: Data is raw fact or figures or entity. When activities in the organization takes place, the effect of these activities need to be recorded which is known as Data.

          For example, the raw material to be purchased may have many facts like type of raw material, vendor name, address, quantity etc. Likewise Organization will have many transactions and entities which are to be recorded.

Information: Processed data is called information.

A database management system (DBMS) is a collection of program that enables user to create and maintain a database. In other words, the systematic organization of data is called database.

The DBMS is hence general purpose software system that facilities the process of defining constructing and manipulating database for various applications.
  •       Defining a database involves specifying the data types, structures and constraints for the data to be stored in the database.
  •      Constructing the database is the process of storing the data itself on some stored medium that is controlled by the DBMS.
  •       Manipulating database includes such functions as querying the database to retrieve specific data updating the database to reflect change and generation of reports from the data.

DBMS Characteristics

The data processing system should have some characteristics to produce the information. Some of the requirements are listed below.
  •  To incorporate the requirements of the organization, system should be designed for easy maintenance.
  •    Information systems should allow interactive access to data to obtain new information without writing fresh programs.
  •  System should be designed to co-relate different data to meet new requirements.
  •  Data should be stored with minimum redundancy to ensure consist in stored data across different application.
  •  An independent central repository, which gives information and meaning of available data, is required.
  •    Integrated database will helps in understanding the inter-relationships between data stored in different applications.
  •  The stored data should be made available for access by different users simultaneously.
  •  Automatic recovery feature has to be provided to overcome the problems with processing system failure.


Advantage of using a DBMS

The following are the advantages of using DBMS.
1.       Controlling redundancy
2.       Restricting unauthorized access.
3.       Providing persistent storage for program object and data structures.
4.       Permitting interface and actions by using rules.
5.       Providing multiple user interfaces.
6.       Presenting complex relationships among data.
7.       Enforcing integrity constraints.
8.       Providing backup and recovery.

E-commerce Security Issues

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First of all e-commerce is surrounded by different issues such as commercial, Network infrastructure, Social and Cultural and Security issues are presented below which are important for successful business. E-commerce security issues are frequently aired in the press and are certainly important. Customers are concerned that the item ordered won’t materialize, or be as described. As (much worse) they worry about their social security number and credit card details being misappropriated. However rare, these things do happen, and customers need to be assured that all e-commerce security issues have been covered. Your guarantees and returns policies must be stated on the website and they must be adhered to. Let us first state the security attacks on e-commerce process and Security goals we want to achieve for successful e-commerce.

Attacks on Security
Security attacks can be classified in the following categories depending on the nature of the attacker.

a)      Passive Attacks
The attacker can only eavesdrop or monitor the network traffic. Typically, this is the easiest form of attack and can be performed without difficulty in many networking environments, e.g. broadcast type networks such as Ethernet and wireless networks.

b)      Active Attacks
The attacker is not only able to listen to the transmission but is also able to actively alter or obstruct it. Furthermore, depending on the attackers actions, the following subcategories can be used to cover to cover the majority to cover the majority of attacks.

c)       Eavesdropping
This is attack is used to gain knowledge of the transmitted data. This is passive attack which is easily performed in many networking environments as motioned above. However, this attack can easily perform in many networking environments. However this attack can easily be prevented by using an encryption scheme to protect the transmitted data.

d)      Traffic Analysis
The main goal of this attack is not to gain direct knowledge about the transmitted data, but to extra information from the characteristics of the transmission, e.g. amount of data transmitted, identity of the communicating nodes etc. This information may allow the attacked to deduce sensitive information, e.g., the roes of the communicating nodes, their position etc. Unlike the previously described attack, this one is more difficult to prevent.

e)      Impersonation
Here, the attacker uses the identity of another node to gain unauthorized access to resource or data. This attack is often used as a prerequisite to eavesdropping. By impersonating a legitimate node, the attacker can try to gain access to the encryption key used to protect the transmitted data. Once, this key is known by the attacker, she can successfully perform the eavesdropping attack.


f)       Modification
This attack modifies data during the transmission between the communicating nodes, implying that the communicating nodes do not share the same view of the transmitted data. An example could be when the transmitted data represents a financial transaction where the attacker has modified the transactions value.

g)      Insertion
This attack involves an unauthorized party, who inserts new data claiming that it originates from a legitimate party. This attack is related to that of impersonation.

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    Risk of e-commerce

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    As e-commerce evolves, it will present huge risks for those who don’t take advantage of it. The main risk of e-commerce is that the business won’t capitalize on all it has to offer, while the competition moves ahead. The traditional supply chain consists of the manufacturer, the distributor; the traditional supply chain consists of the manufacturer, the distributor, the retailer, and the end consumer. E-commerce is changing this linear view of the supply chain. Instead of goods flowing from one participant to the next, this new online marketplace can connect each participant to the end-consumer. For some links in the supply chain, increased access to customers could be dangerous as partners could even become competitors.

    In the physical world today, there are requirements for documents to be in writing and for hand-written signatures. Such requirements need to be translated into the electronic realm with the rapid development of electronic commerce and to resolve questions raised regarding the applicability of such legislation to the unique features of the electronic regime. The advent or e-commerce and the use of the digital medium as an alternative to the physical, have created some novel legal issues where there are no clear answers.

    The users of information technology must have trust in the security of information and communication infrastructures, network and systems, in the confidentiality, integrity, and availability of data on them, and in the ability to prove the origin and receipt of data. For communication and transactions occurring over a faceless network, there is a need or reliable methods to authenticate a person’s identity and to ensure the integrity of the electronically transmitted documents.

    The concepts of a secure electronic record and a secure electronic signature, and the rebuttable presumptions that flow from that status, are thus necessary for a viable system of electronic commerce. In the context of electronic commerce, none of the usual indicators of reliability present in a paper-based transaction (the use of paper, letterhead, etc.) exist, making it difficult to know when one can rely on the integrity and authenticity of an electronic record. This lack of reliability can make proving one’s case in court virtually impossible. Rebuttable presumptions with respect to secure records and secure signatures put a relying partying a position to know, at the time of receipt and/or reliance, whether the message is authentic and the integrity of its contents intact and, equally important, whether it will be able to establish both of these facts in court in the event of subsequent disputes.

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    Benefits of e-commerce

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    Use of e-commerce technologies helps speed up the flow of information and to eliminate unnecessary human intervention; the computer can now accomplish what computers do better than people process routine business transactions quickly and accurately, 24 hours a day. This in turn, frees up people to handle tasks that computers may never be able to do exercising judgment, creativity, and experience to manage exceptions, solve problems and continually improve business processes.

            E-commerce is growing in importance and means unprecedented opportunities for everyone. When a business takes advantage of the power of e-commerce, it will be able to.


            i.            Increase customer satisfaction
    Internet is always open, even on holidays; business is thus always open, 24 hours a day, 7 days a week and 365 days a year. Customers will appreciate the extra access to product updates, shipping details, billing information and more. And since the internet knows no boundaries, customers can shop from home, work, or anywhere they can make a connection. Besides, by connecting the e-commerce and shipping systems, it would be possible to ship products faster and for less money.

          ii.            Increase sales volumes
    The Internet is a new channel to reach new customers. With a web site, a company can automatically become a global provider of goods and services, with an edge over even the largest competitors. Interactive selling is advantageous because a company is no longer limited by shelf-space or inventory concerns but instead offer all products to suit the customers exact specifications.

        iii.            Decrease costs of doing business
    E-commerce helps cut out or streamline processes that eat away profits. For instance exchange of information from advertising to availability updates, can add to the cost of sale. However, the web site can be an efficient, cost-effective communication vehicle. Customers can find timely accurate information in one place when they need it. By using e-commerce, everything from purchase orders to funds transfer can be handled faster and more efficiently. Even payment processing and bookkeeping are easier.


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    Development of e-commerce

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    Now, most of the companies are using e-commerce technology and going to be used. Even small companies have their own web sites, giving details about their profile, Products and services and are moving up in the e-commerce value chain. Companies that were earlier providing access to information on their respective web sites are now engaging themselves in e-commerce practices. Some of the e-commerce practices which are being done by most of the companies for the development of e-commerce technology for them are as follows.

    a) Better Information technology infrastructure

            E-business models are moving from the proprietary ‘Electronic Data Interchange’ (EDI) ‘Specific’ solutions to internet based ‘mass’ solutions. It has more to do with better computer penetration, increase in number of internet users and high-speed connectivity rather than anything else.

    b) Wider acceptance of online payment system

            Online payment mechanism means ‘payment’ and ‘acceptance’ of virtual money. Any such online payment system requires not only the parties transacting business over the Internet but also a ‘payment gateway’ facilitating such transactions. To begin with, it requires use of credit cards and other modes of online payment using advanced technological tools.

              Master Card has recently introduced Site Data Protection Service (SDP), a comprehensive set of global e-business security services that proactively protects online merchants from hacker intrusions. It is a satellite communications network. Also credit card companies have come out with a technology that proactively helps prevents and skimming by using the ‘intrinsic noise’ properties of magnetic strip, which are unique for every card, to differentiate between and original and cloned cards.

    Apart from credit card based transactions, other proprietary online payment systems to initiate the ‘uninitiated’ to shop on the Internet are:

    • Cybercash: Ensuring encrypted passage over the internet for the data card data.
    • E-Cash: Issued online for use over the Internet and is stored in an electronic device such as a chip card of computer memory. The person who has purchased such cash can use it online for making payments.
    • Online Pay: Online Pay allows consumers to shop online without fear of fraud by allowing them to make purchases without giving out information about their credit card or their checking account to the online vendor.
    • Secure Sockets Layers: It is developed by Netscape, which provides privacy, integrity and authentication through digital certificates. Increasing use of Smart Card has also given fillip to the e-commerce activities. Smart cards store all their information on a chip buried within the card. It works as an electronic purse storing digital money, which could be used over public terminals (Web sites, ATMs, Telephone lines) etc. A new system of credit card transactions over the Internet is being currently developed jointly by Visa and MasterCard with technical assistance from the Internet Information system and cryptology companies like Netscape, IBM. It is known to Secure Electronic Transactions (SET). It is expected that in coming years, SET would become the standard of payment over the Internet. Another important development has the adoption of digital signatures as authentication standards providing integrity, confidentiality and non-repudiation of electronic records. It has paved the way for legal recognition of electronic contracts, an extremely important step in giving legal sanctity to online payment system.

    c) Legal recognition to e-commerce practices. 

          Legal recognition of E-commerce practices has come a long way from the initial adoption of UNCITRAL’s Model Law on Electronic commerce by the General Assembly of the United Nations in early 1997. The purpose of the UNCITRAL Model Law on electronic ecommerce is to encourage the use of electronic commerce and to provide nations with model legislation “governing the use of alternative to paper – based methods of communication and storage of information”. It is based on “fundamental-equivalent” approach and extends notions such as “writing”, “signature” and “original” of traditional paper based requirements to a paperless world. It gives legal acceptance to electronic records and digital signatures. Countries, by adopting the UNCITRAL’s Model Law on Electronic commerce have not only given credence to E-commerce laws globally. The most important element is that the nations’ laws on e-commerce have been based on a similar technology platform, i.e. asymmetric cryptography.


    d) Adoption of security standards by the industry

            Business thrives on safety, security and trust whether it is offline or online. The internet being an open, integrated and public system requires far better security coverage than its offline counterpart. It needs an ‘encryption’ technology that provides (i) confidentially (ii) authentication (iii) Integrity (iv) non repudiation and of electronic transactions.

    1. Confidentiality: The idea that the information should be protected from unauthorized internal as well as external users by making it undecipherable. It uses encryption technology to ‘encrypt’ the information in such a way that only an intended user could ‘decrypt’ the information.
    2. Authentication: It means use of encryption technology to identify the sender of originator of the information. Similarly it should be possible to ensure that the message is sent to the person of whom it is meant.
    3. Integrity: It is to verify that the information, which is received, has not been manipulated during its transmission. On retrieval or receipt at the other end of a communication network the information should appear exactly as it was stored or sent by the sender of originator.
    4. Non-repudiation: It is ensure that sender or originator cannot disown information at a later date. Encryption technologies make it possible to bind messages and message acknowledgements with their originators. 

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    Graph Definition

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    A graph is a kind of data structure, which is a collection of nodes, called vertices and line segments called arcs or edges that connect pairs of nodes.

             In the concept of mathematics, a graph G is defined as follows: G=(V,E), where V is a finite, non-empty set of vertices (singular vertex) and E is a set of edges (links between pairs of vertices).  When the edges in a graph have no direction, the graph is called undirected, otherwise called directed.

    Cycle:A cycle is a path consisting of at least three vertices that starts and ends with same vertex. Two vertices are said to be connected if there is a path between them.
    • A directed graph is strongly connected if there is a path from each vertex to every other vertex in the graph.
    • A directed graph is weakly connected if at least two vertices are not connected.
    • Adjacency list: An adjacency list is the representation of all edges or arcs in a graph as a list.
    • Adjacency matrix: The adjacency matrix uses a vector (one-dimensional array) for the vertices and a matrix (two –dimensional array) to store the edges.
    • Depth First Traversal: In the depth first traversal. We process all of the vertex’s descendants before we move to an adjacent vertex. It uses stack to store the nodes.
    • Breadth – First Traversal: In the breadth – first traversal of a graph, we process all adjacent vertices of a vertex before going to the next level. The breadth – first traversal uses a queue rather than a stack. As we process each vertex, we place all of its adjacent vertices in the queue.

    • Spanning trees: A spanning tree of a graph is an undirected tree consisting of only those edges necessary to connect all the nodes in the original graph.
    • Network: A network is a graph that has weights or costs associated with its edges. It is also called weighted graph.
    • Minimum Spanning Tree: This is a spanning tree that covers all vertices of a network such that the sum of costs of its edges is minimum. There are two algorithms which are:
               1)      Kruskals algorithm     2) Prims algorithm

    • Forest: An undirected graph which contains no cycles is called a forest.  A directed acyclic graph is often referred to as dag.
    • Complete graph: A graph is said to be complete if there is an edge between every pair of vertices.
    • Bipartite graph: A graph is said to be bipartite if the vertices can be split into sets V1 and V2. Such there are no edges between two vertices of V1 or vertices of V2.

    • Uniformed search: A problem consists of four parts: the initial state, a set of operators, a goal test function, a path cost function. A path through the state space from the initial state to a goal state is a solution.
    Search algorithms are judged on the basis of completeness, optimally, time complexity and space complexity.
    • Completeness:It is the strategy guaranteed to find a solution when there in one.
    • Time complexity: It is the how long does it take to find a solution.
    • Space complexity: It is the how much memory needs to perform the search.
    • Optimality: Does the strategy find the highest quality solution when there are several different solutions.
    Breadth first search: Expands the shallowest node in the search tree first. It is complete optimal for unit-cost operations, and has time and space complexity of O(b^d). The space complexity makes it impractical in most cases. Using BFS Strategy, the root node is expanded first, then all the nodes generated by the root node are expanded next, and their successors and so on.

    Uniform cost search: Expands the least – cost leaf nod first. It is complete, and unlike breadth-first search is optimal even when operators have differing costs. It’s space and time complexity are the same as BFS.

    Depth- First search: Expands the deepest node in the search tree first. It is neither complete nor optimal, and has time complexity of O(b^m) and space complexity of O(bm), where m is the maximum depth. In search trees of large of finite depth, the time complexity makes this impractical.

    Depth-Limited search: Places a limit on how deep a depth-first search can go. If the limit happens to be equal to the depth of shallowest goal state, then the time and space complexity are minimized.

    Iterative deepening search: Calls depth – limited search with increasing limits until a goal is found. It is completed and optimal, and has time complexity of O(b^d).

    Bidirectional search: Can enormously reduce time complexity, but is not always applicable. Its memory requirements may be impractical. BDS simultaneously search both forward form the initial state and backward from the goal and stop when the two search meet in the middle.


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