What is the Process Control Block? What are its fields?

The task controlling block, switch frame or task struct are the names of one and the same thing that we commonly called as the PCB or the process control block. 

- This data structure belongs to the kernel of the operating system and consists of the information that is required for managing a specific process. 

- The process control block is responsible for manifesting the processes in the operating system. 

- The operating system needs to be regularly informed about resources’ and processes’ statuses since managing the resources of the computer system for the processes is a part of its purpose. 

- The common approach to this issue is the creation and updating of the status table for every process and resource and objects which are relevant such as the files, I/O devices and so on:

1.  Memory tables are one such example as they consist of information regarding how the main memory and the virtual or the secondary memory has been allocated to each of the processes. It may also contain the authorization attributes given to each process for accessing the shared memory areas.

2.   I/O tables are another such example of the tables. The entries in these tables state about the availability of the device required for the process or of what has been assigned to the process. the status of the I/O operations taking place is also mentioned here along with address of the memory buffers they are using.

3.   Then we have the file tables that contain the information regarding the status of the files and their locations in memory.

4. Lastly, we have the process tables for storing the data that the operating systems require for the management of the processes. The main memory contains at least a part of the process control block even though its configuration and location keeps on varying with the operating system and the techniques it uses for memory management.

- Physical manifestation of a process consists of program data areas both dynamic and static, instructions, task management info etc. and this is what that actually forms the process control block. 

- PCB has got a central role to play in process management. 

- Operating system utilities access and modify it such as memory utilities, performance monitoring utilities, resource access utilities and scheduling utilities etc. 

- The current state of the operating system is defined by the set of process control blocks. 

- It is in the terms of PCBs that the data structuring is carried out. 

- In today’s sophisticated operating systems that are capable of multi-tasking, many different types of data items are stored in process control block. 

- These are the data items that are necessary for efficient and proper process management. 

- Even though the details of the PCBs depend up on the system, the common parts can still be identified and classified in to the following three classes:

1.  Process identification data: This includes the unique identifier of the process that is usually a number. In multi-tasking systems it may consists of user group identifier, parent process identifier, user identifier and so on. These IDs are very much important since they let the OS cross check with the tables.

2.   Process state data: This information defines the process status when it is not being executed. This makes it easy for the operating system to resume the process from appropriate point later. Therefore, this data consists of CPU process status word, CPU general purpose registers, stack pointer, frame pointers and so on.

3.   Process control data: This includes process scheduling state, priority value and amount of time elapsed since its suspension. 

What are different kind of browser bugs?

It is a universal fact that every thing in this world is infected with some discrepancies. So does it hold well for the web browsers! This article is here to discuss about the bugs associated with the web browsers.

Till date so many bugs of the web browsers like Mozilla, internet explorer, Netscape, opera and so on have been discovered. Let us check out some of the prominent errors:

Multiple browsers bugs

Bugs discovered under this category are:

(a) Font variant ligatures are not implemented by most of the bugs. The font module level 3 of the CSS defines the property of the font variant ligatures to specify the use of ligatures. Till now no such browser has been developed that supports this property fully.

(b) Font weight is not implemented consistently by the browsers. This font weight property of CSS lays down the specifications regarding the numeric values and key words.

(c) Data tables are not managed properly by the browsers. Most of the table properties are not supported by the browsers.

(d) Layout affected by outlining property.

(e) Styling legend tags

(f) Bugs in Mozilla Firefox
Styling is not applied and problems have been experienced with the horizontal scroll bar.

(g) Bugs in Internet Explorer
When the cursor is hovered over some elements, they did not work properly with the forms; the left origin of the positioning coordinates is incorrectly set.

(h) Bugs in Opera
&rsquo and &isquo entities were not recognizable by the opera, but this was later fixed in the 8th version.

(i) Bugs in Safari
These crashes were reported when : hover :: after was used.

(j) The borders separating the head and the body sections are often placed incorrectly by the opera.

(k) Multi-column ordered list remembering.

(l) Backgrounds show through invisible tables.

(m) Buttons with images cannot be aligned with those having only text.

(n) In some browsers even the fixed elements align along with the adjacent elements.

WHAT CHALLENGES ARE FACED WHILE DEVELOPING A WEBSITE

- When you start developing or designing your web sites choose carefully between the CSS and HTML.

- Don’t go for such an advance version of the languages because if you did then you may run in to the problems with the incompatibility of the browser.

- There is so much of competition going around the whole software market.

- The browser developers are releasing new browsers at very fast pace without even testing them properly which then becomes a headache for the web site designers.

- The new languages being used today like HTML 5 and CSS 3 are now gaining very much popularity though they are pretty much complex then their preceding versions.

- Number of features to be implemented is quite huge which is the major cause of the bugs.

- Whenever you come across a bug, do not forget to report it since it may be so very rare that nobody else would have stumbled up on it.

- One thing you should always remember is to keep the problem in the reduced form as much as possible.

- For doing this you an simply make up a copy of the code and from that remove the java script or CSS files one by one and ultimately you’ll come at a point when the problem will go away.

- Now you add that file and remove the others from the ones that you did previously.

- If you find that the bug is now going away even after removing all the files then it is likely that the bug lies in HTML coding.

- Now after you know that which aspect houses the problem, you need to locate that file or code.

What are major activities in database testing?

Before going to the main topic i.e., the major activities that are carried out in data base testing, we will first have an insight on what is data base testing actually.

WHAT IS DATABASE TESTING?

- Data base testing as it suggests itself, it is the testing of the data or values retrieved from the data base of that software system or application under testing.

- The retrieved data should match exactly with the data mentioned in the records of the data base.

- Data base testing is not an easy thing to carry out.

- It calls for a great need of expertise in reading the data base record tables, writing procedures and queries for the data base.

- Data base testing works well with all sorts of application softwares be it any application written either in SQL or Oracle languages.

- But normally, data base testing finds it way in the testing of applications that work with all sorts of sensitive data like finance, banking or health insurances etc.

- Such applications require extensive data base testing since any error in the retrieved data can cause the users lot to suffer.

MAJOR ACTIVITIES OF DATABASE TESTING
Now we are going to discuss about the working of the data base testing or what all are the major activities taking place in a data base testing.

- A lot of understanding and knowledge of the software system or application under the testing is required i.e., the tester needs to know all about the type of data base being used by the software system or application.

- All the existing data tables in the application data base are figured out.

- All the possible queries are written for the figured out tables to be executed.

- All the tables are tested individually for the verification and validation of the data contained in them.

- For complex data bases the queries are obtained from the developer and the functionalities are tested.

- The data base of a software system or application is indeed its back bone and needs to be tested thoroughly.

- In a data base testing not only the data base undergoes testing, but also the features and functionality of the software system or application.

- As if this is not enough, all the actions taking place like deletion or addition are also tested.

- The added values or data are checked against the records of the data base i.e., whether or not they are exactly same.

- The deleted is checked for whether or not it has been really deleted from the data base.

- Every action being performed is tested for its efficiency as it will affect the overall well being of the data base.

- These days with the introduction of the business logic, the data bases have become more complex.

- Though the business logic makes the whole data base complex in nature, it cannot be neglected since it plays a very crucial role in the implementation of the applications.

- After the implementation of the business rules or logic, the data base values are again checked for their correctness.

- The coupling of the data bases to the libraries also poses a problem for the data base testing besides the following:

1. Data base schemas
2. Data base tables
3. Verification of the data base after every execution of test cases.
4. Cleaning up of the data base for every new test case execution.
5. Carrying out the whole data base testing manually is absolutely impossible or perhaps a nightmare.
6. Writing short test codes that are easy to understand.

One needs to carry out data base testing very carefully and with understanding since any faltering can disrupt the whole testing process.

Estimation Techniques - For Web Engineering Projects

Early estimation is required during planning even though there is a huge chance that these are proven wrong. Some uncertainty is unacceptable and some solid techniques and concrete procedures help reduce the inaccuracy of estimates.

Estimating techniques for web engineering projects adapt the agile process model. Along with the agile estimation approach, a modified function point (FP) measure can be used to develop an estimate for a web application. Roetzheim suggests for web application estimation, the information domain values while adapting function points are:

- Inputs include maintenance screen, input screen or form or each tab using a tab notebook.
- Outputs include static web page, dynamic web page script, each report whether web based or administrative in nature.
- Tables include logical tables in database, each XML object if XML is used to store data.
- Interfaces are logical files into our out of the system boundaries.
- Queries are a message oriented interface and they are externally published.

According to Mendes:
The best way to determine the volume of the web application is by :
- predictor variables that are associated with application like page count, function count, media count,
- web page characteristics like page complexity, linking and graphic complexity,
- media characteristics like media duration,
- functional characteristics like code length.

Empirical estimation models for:
- total project effort
- page authoring effort
- media authoring effort
- scripting effort
can be evaluated by using these measures.

How to design conventional components - Graphical Design Notation and Tabular Design Notation

There were some logical constructs developed from which any program could be formed. Each construct has a logical structure. The constructs are sequence, condition, and repetition.
- Sequence implements processing the steps that are essential in the specification of any algorithm.
- Condition provides the facility for selected processing based on some logical occurrence.
- Repetition allows for looping.
Structured programming is a design technique that constrains logic flow to three constructs: sequence, condition and repetition. The structured constructs were supposed to limit the procedural design of software to a small number of predictable operations.

GRAPHICAL DESIGN NOTATION
Activity diagram allows a designer to represent sequence,condition and repetition. Flowchart, like an activity diagram, is quite simple pictorially.
The dogmatic use of only structured constructs can introduce inefficiency when an escape from a set of nested loops or nested conditions is required. Additional complication of all logical tests along the path of escape can hinder the control flow, increase the possibility of error and have a negative impact.
There are two options:
- procedural representation is redesigned so that escape branch is not required at a nested location.
- structured constructs are violated in a controlled manner; that is , a constrained branch out of the nested flow is redesigned.

TABULAR DESIGN NOTATION
Decision tables translates actions and conditions in a tabular form. It is difficult to misinterpret. A decision table is divided into quadrants:
- Upper left quadrant: contains a list of all conditions.
- Lower left quadrant: contains a list of all actions that are possible based on combinations of conditions.
- Right hand quadrant: a matrix that indicates condition combinations and corresponding actions. Each column of matrix may be interpreted as a processing rule.

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Introduction to Relational Databases

Relational databases are probably the most common type of database used for general-purpose tasks. In a relational database, information is grouped according to its type, generally in tables (see below). For example, in a database designed to hold fleet information you may include a table of employees and a table of vehicles.
- In addition to separating information according to its data structure, a relational database allows relationships to be created. A relationship defines a possible link between data types; the actual linkage of data is dependent upon the information held.
- Relational databases use the concept of normalization. Normalization is a design technique that minimizes the duplication of information. It also reduces the risk of errors. By using relationships, the duplication required can be lessened or eliminated completely.
A Relational model is the basis for any relational database management system (RDBMS). A relational model has mainly three components:
- A collection of objects or relations.
- Operators that act on the objects or relations.
- Data integrity methods.

Elements of a Relational Database Schema :
There are several key elements to a relational database. Each of these forms a part of the database's schema. The schema is the logical data model that determines the information that may be stored in the database and how it is to be arranged. To design a database we need three things:
- Table : A table is one of the most important ingredient to design the database. It is also known as a relation, and is a two dimensional structure used to hold related information. A database consists of one or more tables.
- Rows : A table contains rows. Rows are collection of instance of one thing.
- Columns : A table contains the columns. Columns contains all the information of a single type. Each column in a table is a category of information referred to as a field.
- Indexes : One of the greatest benefits of holding information in a database is the ability to quickly retrieve it. When querying a database, it is possible to apply criteria to ask for a specific set of rows.
- Keys : A primary key is a single column, or group of several columns (compound key), that can be used to uniquely identify rows in a table. Each table in a database may have a single primary key. Once defined, no two rows in the table may contain matching data in the primary key columns. Foreign keys are used when defining relationships between tables. A foreign key is a single column, or group of columns, in a table that reference the primary key in another table. This creates a link between the two tables.
- Constraints : Constraints are rules that are applied to the information in a database. These are usually used to enforce business rules upon the tabular data.
- Views : Views provide the useful concept of virtual tables. A view gathers specific information from one or more sources and presents it in the format of a single table. The information may be filtered within the view to remove unnecessary information.
- Stored Procedures : A stored procedure is a predefined set of statements that can be executed when required. Stored procedures provide the main means of creating programs within SQL Server databases.

Domain and Integrity Constraints :
* Domain Constraints
o limit the range of domain values of an attribute
o specify uniqueness and `nullness' of an attribute
o specify a default value for an attribute when no value is provided.
* Entity Integrity
o every tuple is uniquely identified by a unique non-null attribute, the primary key.
* Referential Integrity
o rows in different tables are correctly related by valid key values (`foreign' keys refer to primary keys).