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at February 03, 2020 0

Scope of Variables

All variables in a program may not be accessible at all locations in that program. This depends on where you have declared a variable.
The scope of a variable determines the portion of the program where you can access a particular identifier. There are two basic scopes of variables in Python −
  • Global variables
  • Local variables


Global vs. Local variables

Variables that are defined inside a function body has a local scope, and those defined outside have a global scope.
This means that local variables can be accessed only inside the function in which they are declared, whereas global variables can be accessed throughout the program body by all functions. When you call a function, the variables declared inside it are brought into scope. Following is a simple example −

total = 0; # This is global variable.
# Function definition is here
def sum( arg1, arg2 ):
   # Add both the parameters and return them."
   total = arg1 + arg2; # Here total is local variable.
   print "Inside the function local total : ", total
   return total;

# Now you can call sum function
sum( 10, 20 );
print "Outside the function global total: ", total
When the above code is executed, it produces the following result −
Inside the function local total: 30
Outside the function global total :  0


The return statement

The return statement is used to exit a function and go back to the place from where it was called.The statement return [expression] exits a function, optionally passing back an expression to the caller. A return statement with no arguments is the same as return None.

Syntax of return
return [expression_list]
This statement can contain an expression which gets evaluated and the value is returned. If there is no expression in the statement or the return statement itself is not present inside a function, then the function will return the None object.
For example:-
All the above examples are not returning any value. You can return a value from a function as follows −
# Function definition is here
def sum( arg1, arg2 ):
   # Add both the parameters and return them."
   total = arg1 + arg2
   print "Inside the function : ", total
   return total;

# Now you can call sum function
total = sum( 10, 20 );
print "Outside the function : ", total
When the above code is executed, it produces the following result −
Inside the function: 30

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at February 03, 2020 0

Digital signatures

A digital signature or digital signature scheme is a mathematical scheme for demonstrating the authenticity of a digital message or document. A valid digital signature gives a recipient reason to believe that the message was created by a known sender such that they cannot deny sending it (authentication and non-repudiation) and that the message was not altered in transit (integrity). Digital signatures are commonly used for software distribution, financial transactions, and in other cases where it is important to detect forgery or tampering.
A digital signature (NOT a digital certificate) is an electronic signature that can be used to authenticate the identity of the sender of a message or the signer of a document, and possibly to ensure that the original content of the message or document that has been sent is unchanged. Digital signatures are easily transportable, cannot be imitated by someone else, and can be automatically time-stamped. The ability to ensure that the original signed message arrived means that the sender cannot easily repudiate it later.
A digital signature can be used with any kind of message, whether it is encrypted or not, simply so that the receiver can be sure of the sender's identity and that the message arrived intact. A digital certificate contains the digital signature of the certificate-issuing authority so that anyone can verify that the certificate is real.

Digital certificate

An attachment to an electronic message used for security purposes. The most common use of a digital certificate is to verify that a user sending a message is who he or she claims to be, and to provide the receiver with the means to encode a reply.
An individual wishing to send an encrypted message applies for a digital certificate from a Certificate Authority (CA). The CA issues an encrypted digital certificate containing the applicant's public key and a variety of other identification information. The CA makes its own public key readily available through print publicity or perhaps on the Internet.
The recipient of an encrypted message uses the CA's public key to decode the digital certificate attached to the message, verifies it as issued by the CA and then obtains the sender's public key and identification information held within the certificate. With this information, the recipient can send an encrypted reply. The most widely used standard for digital certificates is X.509.

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at February 02, 2020 0

NETWORK SECURITY

Network security consists of the provisions and policies adopted by a network administrator to prevent and monitor unauthorized access, misuse, modification, or denial of a computer network and network-accessible resources. Network security involves the authorization of access to data in a network, which is controlled by the network administrator. Users choose or are assigned an ID and password or other authenticating information that allows them access to information and programs within their authority.

Network security concerns:

Secrecy
Secrecy has to do with keeping information out of the hands of unauthorized users. This is what usually comes to mind when people think about network security.

Authentication
Authentication deals with determining whom you are talking to before revealing sensitive information or entering into a business deal.

Non-repudiation and Integrity Control
Non-repudiation deals related with signatures. Assurance that a message received was really the one sent and not something that a malicious adversary modified in transit or concocted.

Physical Security
It is the most fundamental of all security levels because it deals with securing your technology equipment from damage or theft, protecting it against accidental power surges, and the like.

Common Network security risks (attacks): -

wiretapping
Port scanner
Idle scan
Denial-of-service attack
Spoofing
Man in the middle
ARP poisoning
Smurf attack
Buffer overflow
Heap overflow
Format string attack
SQL injection
Cyber Attack

Network security management:

AAA (Tripple – A: Authentication, Authorization, Auditing)
Firewall & UTM (Unified Threat Management) system
Cryptography and encryption
VPN (Virtual Private Network)
Antivirus
Policies and guidelines
Physical security

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at January 26, 2020 0

HISTORY OF HTML

In 1980, physicist Tim-Berners-Lee, a contractor at CERN proposed internet- based hypertext system.
It was formally defined by Internet Engineering Task Force (IETF).
After development of Html, IETF created Html working group. Html working group developed Html 2.0 in 1995.
By the combined work of World Wide Web Consortium (W3C) and Web Hypertext Application Technology Working Group (WHATWG) released a greater number of advanced Html versions Html 3.2 in 1997, Html 4.0 in 1997, Html 4.01 in 1999
After a long interval, Html released a new version called Html5 in 2014. Html5 enhances the web pages to a new world.
In 2016 Html 5.1 version was released by W3C.
Now lets have brief history about versions of html that we have till now.

HTML 1.0

HTML 1.0 was the first release of HTML to the world. Not many people were involved in website creation at the time, and the language was very limiting. There really wasn’t much you could do with it bar getting some simple text onto the web.

HTML 2.0

HTML 2.0 included everything from the original 1.0 specifications but added a few new features to the mix. HTML 2.0 was the standard for website design until January 1997 and defined many core HTML features for the first time.

HTML 3.0

More and more people were getting into the HTML game around now, and while the previous standards offered some decent abilities to webmasters (as they became known), they thirsted for more abilities and tags. They wanted to enhance the look of their sites.
This is where trouble started. A company called Netscape was the clear leader in the browser market at the time, with a browser called Netscape Navigator. To appease the cries of the HTML authors, they introduced new proprietary tags and attributes into their Netscape Navigator browser. These new abilities were called Netscape extension tags. This caused big problems as other browsers tried to replicate the effects of these tags so as not to be left behind but could not get their browsers to display things the same way. This meant that if you designed a page with Netscape ETs, the page would look bad in other browsers. This caused confusion and irritation for the markup pioneers.
At this time, a HTML working group, led by a man named » Dave Raggett introduced a new HTML draft, HTML 3.0. It included many new and improved abilities for HTML, and promised far more powerful opportunities for webmasters to design their pages. Sadly, the browsers were awfully slow in implementing any of the new improvements, only adding in a few and leaving out the rest. Partly,
this failure can be attributed to the size of the overhaul; and so the HTML 3.0 spec was abandoned.
Thankfully, the people in charge noted this and so future improvements were always designed to be modular. This meant they could be added in stages, which makes it easier on the browser companies.

HTML 3.2

The browser-specific tags kept coming, and it became increasingly apparent that a standard needed to be found. To this end, the » World Wide Web Consortium (abbreviated to the W3C) was founded in 1994 to standardize the language and keep it evolving in the right direction. Their first work was code-named WILBUR, and later became known as » HTML 3.2. This was a toned-down change to the existing standards, leaving many of the big steps forward for later versions. Most of the extensions tags that had been introduced by Netscape (and to a lesser-extent, Microsoft) did not make it into these new standards. It soon caught on and became the official standard in January ’97, and today practically all browsers support it fully.

HTML 4.01

HTML 4.0 was a large evolution of the HTML standards, and the last iteration of classic HTML. Early in development it had the code-name COUGAR. Most of the new functionality brought in this time is from the ill-fated HTML 3.0 spec, as well as a host of trimmings on old tags and support for HTML’s new supporting presentational language, cascading stylesheets.
HTML 4.0 was recommended by the W3C in December ’97 and became the official standard in April 1998. Browser support was undertaken surprisingly earnestly by Microsoft in their Internet Explorer - browser, and the market-leading IE5 (and current successor IE6) have excellent support for almost all of the new tags and attributes. In comparison, Netscape’s terribly flawed Navigator 4.7 was inept when it came to HTML 4.0 and even basic CSS. Modern browsers however, are a vast improvement.
Once HTML 4.0 had been out for a little while, the documentation was revised and corrected in a few minor ways and was entitled HTML 4.01; the final version of the specification.

XHTML 1.0 (Extensible hypertext markup language)

Close to the beginning of the 21st century the W3C issued their » specifications of XHTML 1.0 as a recommendation. Since January 26, 2000 it stands as the joint-standard with HTML 4.01. XHTML marks a departure from the way new specs have worked — it is an entirely new branch of HTML, incorporating so that code must be properly written if it is to work once it reaches the reader’s browser. There weren’t many new or deprecated tags and attributes in XHTML, but some things changed with a view of increased accessibility and functionality. It’s mainly just a new set of coding rules.

HTML5

After HTML 4.01 and XHTML 1.0, the guys who were in control of HTML’s direction got sidetracked working on a new proposal for XHTML 2. At the same time, clever web developers were innovating constantly, hacking new functionality into websites and browsers. The path that XHTML 2 was taking started to look both boring and unrealistic, and it became pretty clear that a new approach was needed.
It was around this time that a bunch of pragmatic web technology fans, browser programmers and specification writers started building something of their own, outside of the usual W3C procedures. They called themselves the Web Hypertext Application Technology Working Group (WHATWG). After some soul-searching, the W3C decided that HTML was still the future of the web. XHTML 2 was discontinued and HTML5 became the new specification that everyone’s effort should be poured into.

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at January 21, 2020 0

Computer-aided Software Engineering (CASE) Tools

Computer-aided systems engineering (CASE) tools are the software programs that help the development team do their jobs more efficiently and more effectively. These tools support the drawing and analysis of system models. Some CASE tools also provide prototyping and code generation capabilities. Some examples are: Oracle’s Designer 2000, Rational’s Rose, Platinum’s Erwin, Popkin’s System Architect 001, and Visible System’s Visible Analyst.

At the center of any CASE tool’s architecture is a developer’s database called a CASE repository. CASE repository is a system developer’s database where developers can store system models, detailed description and specification, and other products of system development. It is also called dictionary or encyclopedia.

Around the CASE repository is a collection of tools or facilities for creating system models and documentation. These facilities generally include:
  1. Diagramming tools –These tools are used to draw system models.
  2. Dictionary tools – These tools are used to record, delete, edit, and output detailed documentation and specification.
  3. Design tools – These tools are used to construct system components including system inputs and outputs. These are also called prototyping tools.
  4. Documentation tools – These tools are used to assemble, organize, and report on system models, descriptions and specifications, and prototypes.
  5. Quality management tools – These tools are used to analyze system models, descriptions and specifications, and prototypes for completeness, consistency, and conformance to accepted rules of methodologies.
  6. Design and code generator tools – These tools automatically generate database designs and application programs or significant portions of those programs.

Computer-aided Software Engineering (CASE) Tools | SAD

Today’s CASE tools provide two distinct ways to develop system models – forward engineering and reverse engineering. Forward engineering requires the system analyst to draw system models, either from scratch or from templates. The resulting models are subsequently transformed into program code. Reverse engineering, on the other hand, allows a CASE tool to read existing program code and transform that code into a representative system model that can be edited and refined by the systems analyst. CASE tools that allow for bi-directional, forward and reverse engineering are said to provide for “round-trip engineering”.

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at January 20, 2020 0

Different Approaches to Improving Information Systems Development

Several different approaches have been developed in the continuous effort to improve the systems analysis and design process. The two important approaches are prototyping and joint application development (JAD).


Prototyping

Prototyping is a form of rapid application development (RAD). Prototyping is a rapid, iterative, and incremental process of systems development in which requirements are converted to a working system that is continually revised through close work between the development team and the users. We can build a prototype with any computer language or development tool, but special prototyping tools have been developed to simply the process. A prototype can be developed with some fourth-generation language (4GL), with the query and screen and report design tools of a database management system, and with tools called computer-aided software engineering (CASE) tools.
Different Approaches to Improve Information Systems Development | SAD
Prototyping

In prototyping, the analyst works with users to determine the initial or basic requirements for the system. The analyst then quickly builds a prototype. When the prototype is completed, the users work with it and tell the analyst what they like and do not like about it. The analyst uses this feedback to improve the prototype and takes the new version back to the users. This iterative process continues until the users are relatively satisfied with what they have seen.
Ideally, the prototype serves as a mechanism for identifying information system requirements. In this case, we throw away the prototype (also called throwaway prototype) after identifying requirements. The actual information system is developed with an eye toward quality and maintainability based on the requirements.


Advantages:

  1. Useful for projects in which user requirements are uncertain or imprecise.
  2. It encourages active user and management participation.
  3. Projects have higher visibility and support because of the extensive user involvement.
  4. Users and management see working, software-based solutions more rapidly.
  5. Errors and omissions tend to be detected earlier in prototypes.
  6. Testing and training are natural by-products.
  7. It is more natural process.
  8. It is most popular for small to medium-size projects.


Disadvantages:

  1. It increases lifetime cost to operate, support and maintain the system.
  2. It can solve the wrong problems since problem analysis is abbreviated or ignored.
  3. The product may have less quality because of speed in development.


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at January 19, 2020 0

Developing Information Systems and System Development Life Cycle (SDLC)

Most organizations use a standard set of steps, called a systems development methodology to develop and support their information systems. It is a standard process followed in an organization to conduct all the steps necessary to analyze, design, implement, and maintain information systems. And systems development life cycle (SDLC) is the traditional methodology used to develop, maintain, and replace information systems. It includes different phases as shown in the figure below. This representation of SDLC is sometimes referred to as the waterfall model or classic life cycle.
 
Developing Information Systems and System Development Life Cycle (SDLC)
Fig: The systems development life cycle

The first phase is called planning. In this phase, someone identifies the need for a new or enhanced system. These needs are then analyzed, prioritized and arranged into a plan for the IS department. Here, a potential information systems project is explained and an argument for continuing or not continuing with the project is presented; a detailed plan is also developed for conducting the remaining phases or the SDLC for the proposed system.
The next phase is called analysis. During this phase, the analyst studies the current system and proposes alternative replacement systems. Here, the analyst thoroughly studies the organization’s current procedures and the information systems used to perform organizational tasks. The analyst work with users to determine what the users want from a proposed system. The analyst carefully studies any current systems, manual and computerized, that might be replaced or enhanced as part of this project. The analyst studies the requirements and structures them according to their interrelationships and eliminates any redundancies; generates alternative initial designs to match the requirements; compare these alternatives to determine which best meets the requirements within the cost, labor, and technical levels the organization is willing to commit to the development process. The output of this phase is a description of the recommended alternative solution. Once the recommendation is accepted by owners, you can begin to make plans to acquire any hardware and system software necessary to build or operate the system as proposed.
The next phase is called design. During this phase, you convert the description of the recommended alternative solution into logical and then physical system specification. Here, you must design all aspects of the system form input and output screens to reports, databases, and computer processes. Logical design is the part of the design process that is independent of any specific hardware or software platform. Theoretically, the system could be implemented on any hardware and systems software. Physical design is the part of the design phase in which the logical specifications of the system from logical design are transformed into technology-specific details from which all programming and system construction can be accomplished.
The next phase is called implementation. In this phase, the information system is coded, tested, installed, and supported in the organization. During coding, programmers write the programs that make up the information system. During testing, programmers and analysts test individual programs and the entire system in order to find and correct errors. During installation, the new system becomes a part of the daily activities of the organization. Implementation activities also include initial user support such as the finalization of documentation, training programs, and ongoing user assistance.
The final phase of SDLC is called maintenance. In this phase, information system is systematically repaired and improved. When a system is operating in an organization, users sometimes find problems with how it works and often think of better ways to perform its functions. Also the organization’s needs with respect to the system change over time. In maintenance, you make the changes that users ask for and modify the system to reflect changing business conditions. Waterfall model is the oldest and the most widely used paradigm for information systems development. While it does have weaknesses, it is significantly better than a haphazard approach. This model is suitable for the projects in which user requirements are certain and precise. The problems that are sometimes encountered with the linear sequential model are:
Changes can cause confusion as the project team proceeds.
It is often difficult for the customer to state all requirements explicitly. The linear sequential model requires this and makes difficulty to respond to changing customer requirements.
A working version of the system will be available to customers late in the project time-span. A major blunder, if undetected until the working program is reviewed, can be disastrous.
The linear nature of the classic life cycle leads to “blocking states” in which some project team members must wait for other members of the team to complete dependent tasks.
User involvement is limited.

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at January 18, 2020 0

Preparing Career as a Systems Analyst

System analysts are the key individuals in the information system development process. To succeed as a system analyst, you will need to develop the following skills.
  1. Working Knowledge of Information Technology: This is the technical skill. The analyst must be aware of both existing and emerging information technology. Such knowledge can be acquired by college courses, seminars and training programs.
  2. Computer Programming Experience and Expertise: This is also a technical skill needed by systems analysts. Most system analyst need to be proficient in one or more high level programming language.
  3. General Knowledge of Business Processes and Terminology: Most of the systems today are business related and the systems analysts must be able to communicate with business experts to gain understanding of their problems and needs. So, this skill is must. To develop this skill, the system analyst should have knowledge about the courses like accounting, finance, business law and ethics, economics, manufacturing, marketing, operations management, human resource management, organizational behavior etc.
  4. General Problem-Solving Skill: The systems analyst must be able to take a large business problem, break down that problem into its component parts, analyze the various aspects of the problem, and then assemble into an improved system to solve the problem. To develop this skill, a system analyst should have knowledge about critical thinking and reasoning.
  5. Good Interpersonal Communication Skill: To know the user requirements, an analyst must be able to communicate orally and in writing. To develop this skill, the courses like business and technical writing, business and technical speaking, interviewing and listening will be effective.
  6. Good Interpersonal Relations Skill: The systems analysts should interact with all the stakeholders in the information system development project. To do this they must have this skill. To improve this skill, the analyst should have knowledge about the courses like teamwork, principles of persuasion, managing change and conflict, and leadership.
  7. Flexibility and Adaptability: No two projects are alike. So, a successful system analyst must learn to be flexible and to adapt to unique challenges and situations.
  8. Character and Ethics: The system analyst should have strong character and a sense of right and wrong. This is needed to hide the sensitive and confidential facts and information of an organization.
  9. System Analysis and Design Skill: All systems analysts should know concepts and principles, tools, and techniques of information systems development.


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