Example Of Primary Key Computer Science Essay

Example Of Primary Key Computer Science Essay Database is a structure that is generally divided in two respects, namely a flat database and a relational database. Relational database easier to understand than the flat database. Because relational database has a simple design and it is easy to do data operations. Database also has a relational structure found in tables to store data. On each table is it consists of columns and rows and a column to define the type of information that should be saved. Basically the database is very useful when the time to retain the information that will be categorized logically. For example, if you want to save the information on the data, the database enterprise or school, it can be in a group with matters in business become more tables. In the database there is some relationship, the relationship is as one to one, many to many, one to many, Primary Key The key is a set of columns that can be used to identify or access a particular row or rows. Identified key explanatory tables, indexes, constraints or reference. The same column can be part of more than one key. A unique key is a key that is constrained so that no two values à ¢Ã¢â€š ¬Ã¢â‚¬ ¹Ãƒ ¢Ã¢â€š ¬Ã¢â‚¬ ¹are the same. Unique key columns cannot contain NULL valuesà ¢Ã¢â€š ¬Ã¢â‚¬ ¹Ãƒ ¢Ã¢â€š ¬Ã¢â‚¬ ¹. For example, the column number of employees can be defined as a unique key, because each value in column identifies only one employee. No two employees can have the same number of workers. The mechanism used to enforce uniqueness of the so-called index unique key. Unique index table is a column, or a collection of ordered columns, each of which identifies value (specify function) unique rows. A unique index can contain NULL valuesà ¢Ã¢â€š ¬Ã¢â‚¬ ¹Ãƒ ¢Ã¢â€š ¬Ã¢â‚¬ ¹. The key is one unique key defined on the table, but was selected as the first important key. There can be only one primary key on the table. A primary index is automatically created for the primary key. The main index used by the database manager for efficient access to table rows, and allows the database manager to enforce the uniqueness of the primary key. (You can also specify non-primary index key columns efficiently access the data when processing the query.) If the table does not have a natural unique key, or if the order of arrival is a method used to distinguish unique rows, use a time stamp as part of the key can help. Example of Primary Key PROJNO (Primary Key) PROJNAME DEPTNO MA2100 Weld Line Automation D01 MA2110 Weld Line Programming D11 Example 1 If each column in the table contains duplicate valuesà ¢Ã¢â€š ¬Ã¢â‚¬ ¹Ãƒ ¢Ã¢â€š ¬Ã¢â‚¬ ¹, it cannot determine the key with just one column. A key with more than one column is a composite key. The combination of column values à ¢Ã¢â€š ¬Ã¢â‚¬ ¹Ãƒ ¢Ã¢â€š ¬Ã¢â‚¬ ¹should define a unique entity. If a composite key cannot be easily defined, it can also be considered to create a new column with unique valuesà ¢Ã¢â€š ¬Ã¢â‚¬ ¹Ãƒ ¢Ã¢â€š ¬Ã¢â‚¬ ¹. EMPNO (Primary Key) PROJNO (Primary Key) ACTNO (Primary Key) EMPTIME EMSTDATE (Primary Key) 000250 AD3112 60 1.0 1982-01-01 000250 AD3112 60 5 1982-02-01 000250 AD3112 70 5 1982-02-01 Foreign Key A foreign key is a field in a table corresponding relationship with the other candidate key table. Foreign keys can be used to cross-reference table. For example, suppose we have two tables, customer that includes all customer data, and the order table that includes all customer orders. Intention here is that all orders must be associated with a client who is in the customer table. To do this, we will place a foreign key in the order table and it relates to the key customer table. Identifying foreign key column or set of columns in a table that refers to a column or set of columns in another table. Column in the table must reference the key pillars or other super key in the referenced table. Value in a reference column line must occur in a single row in the referenced table. Thus, a row in the reference table cannot contain values à ¢Ã¢â€š ¬Ã¢â‚¬ ¹Ãƒ ¢Ã¢â€š ¬Ã¢â‚¬ ¹that do not exist in the referenced table (except potentially null). In this way a reference can be made to link information together and it is an important part database normalization. Various rows in the table reference may refer to the same row in the referenced table. Most of the time, it reflects a (parent table or reference table) to many (child table, or referencing table) relationship. Example Foreign Key Below is an example of the relationship between the Company and also schedules, Contact. Tables in the company is the parent of a link. In child contact schedule, Field CompanyID the table to show the contact contacted the company owned. The role of the Son (Multiplicity) Diversification foreign key defines how many records in the child table can link to records in the master table. In the above example the childs diversity since a company can have any number of contacts. Example Primary Key Foreign Key Relationship It have a Primary Foreign Key, in this figure it have a relationship between this two keys. e.g. One to One , One to Many , Many to Many. Primary key. This is indicated by the Primary Key field equivalent to the schedule. this shows that the field that identifies a unique record. For example, Product_ID product and ORDER_ID for Order the values à ¢Ã¢â€š ¬Ã¢â‚¬ ¹Ãƒ ¢Ã¢â€š ¬Ã¢â‚¬ ¹that are normally produced by the field is Auto-rise. they do not have any intrinsic meaning and only integers are automatically generated one by one. Primary Key and Foreign Keys. This indicated that the PF with the field in the table. In this case, the field is also created as a key example of this attitude in the Schedule of Key, Primary Key in Table Customer_Orders_Products is a composite key, consisting of two fields. The product_id is the Primary Key in the table Products, and ORDER_ID is the Primary Key in the table Customer_Orders. One-to-Many Relationship. One-to-Many very common in the real world, and it is very easy to read that A Parents can have a lot of children. In this figure shows that, One Product can be attributed to Customer_Orders_Products the Many. The line between product and Customer_Orders_Products is continuous line (not small dotted lines). This means that the product_id field is the Primary Key in Table Customer_Orders_Products. A dotted line will show the existence of a Foreign Key. Many-to-Many Relationships. Relationship Many-to-Many very important in the real world, and being able to see them all around us every day. For example, many customers may order the same product. Many products can be ordered by the same customer. This is called Relationship Many-to-Many. It can not be implemented directly in the Database Table relationships. The solution is to create an intermediate table that records all the combinations that exist between the Customer and Product. For example, if a customer who ordered three products, then there will be three records for that customer in an intermediate table. Low key combination to be a parent table primary key intermediate in this table. We also need to allow for comments like Make it stronger,. If we get to the right database structure, then it is very easy to extend it. Question 2 Explain the main characteristics and advantages of the following terms. a ) Relational Database b) Object Oriented Database c) Object Relational Database Relational Database Can be connected to a database with a collection of data items is strongly recommended as a set and the name of the Minister of Finance official explained from Any data easily accessible. A database was created using the model relations relationship. The software used in database relations database management system called Relations. A relationship database is the preferred choice in storing data, as compared to other models such as the hierarchical database model or network model. The first database is been commenced in 1970, namely by Edgar Codd. Advantages of Relational Database Avoid Error There is only a single storage location for any piece of information, so: data update is easy without having to change the same information in 15 different files. info is always up to date there is no chance of remaining old data in some forgotten file. Number and date: no typos such as 10, 10, 10, not 10. avoid problems such as data type in Excel dreaded syndrome. avoid unwanted text-to-date conversion like November 12 to be November 12 1900. Error checking data as they are entered: validated data on data entry, to filter the impossible data can be cross-checked against existing information. Manipulate Data With databases it can combine different data easily. No more error-prone cut-and-paste to force data into different formats. Do away with all intermediate Excel spreadsheet that is often generated when manipulating data. (And which you often darent delete just in case they contain important information.) Data manipulation is done by using a query. This means Structured Query Language, SQL, to merge, update and manage data, but most users do not need to know any SQL to perform complex tasks. In Microsoft Access, for example, Visual Query Builder provides a simple, intuitive interface makes most queries. Visualize Data A database is being adjusted can reveal new areas for investigation to present large quantities of data in an intuitive form. Often the patterns become apparent only by flicking through data. With this special database it is possible in new ways: data from many different sources can be brought together and displayed quickly and and fast. Integrate with analysis Ends with an Excel file to a multi-analysis, each subtlety different? Never sure that the correct file is not delete any, just in case. With a relational database, this is the dilemma of the past. Your data set for analysis is created using queries stored in the database. No copy is made of data, but instead you link to query directly from the statistics. Object Oriented Database Reduced Maintenance The main goal of the object-oriented development is a guarantee that the system will enjoy a longer life while having maintenance costs much less. This is because most of the processes in the system contained, behavior that can be reused and will be included in the most recent behavior. The ultimate goal is for the new object-oriented development Real World Modeling Objects operational system is very prone to model the real world in a more complete fashion than do traditional methods. Objects that have been organized into a class of objects, object-related behaviors. Based on the object, rather than on data and processing only Improved Reliability and Flexibility Object-oriented system to be far more reliable than traditional systems, especially in the new behavior can be built from existing objects. Because objects can be dynamically called and accessible, new objects can be created at any time. New objects can inherit data attributes from one, or many other objects. Behavior that can be inherited from the super-class, and novel behavior can be added without performing the functions of the existing system. Object Relational Database Database Object capabilities can be expanded with additional ties and new data types, access methods and functions available in object oriented programming. it can add character string with alpha-numeric data types. Complex data types can combine features of data types that already exist in the database. here it is able to determine the data type of text containing desired time or with the number of bytes used to create user defined data types can be opaque or own. it can also add user-defined virtual processors. Encapsulation By using encapsulation of database object you want to contact in the form of a table. For example, Table 1 includes the name, address, phone number and email address for contact. Through class encapsulating Contacts, it just combines all this information in a table on this one. So when you query the database for this information, you generate a report in a style designed to include all of this information. Appendix PROJNO (Primary Key) PROJNAME DEPTNO MA2100 Weld Line Automation D01 MA2110 Weld Line Programming D11 EMPNO (Primary Key) PROJNO (Primary Key) ACTNO (Primary Key) EMPTIME EMSTDATE (Primary Key) 000250 AD3112 60 1.0 1982-01-01 000250 AD3112 60 5 1982-02-01 000250 AD3112 70 5 1982-02-01

Midsummer Night’s Dream Theme Essay

One of the play’s main themes is the difference between perception and reality. The idea that things are not necessarily what they seem to be is at the heart of A Midsummer Night’s Dream, and in the very title itself. â€Å"Reality is merely an illusion, although a very persistent one.† These words were spoken by Albert Einstein who, among the many other things he thought about, considered the very thin line between what we see and feel and what is real. Many great thinkers have pondered the relationship between the senses and reality. How much of the world truly exists and how much of it is only what is in one’s mind? Among these thinkers was one particular writer named William Shakespeare. A man who enjoyed pointing out the gullibility of mankind, sometimes tragically and sometimes playfully, wrote a masterpiece of theater exploring that very concept. A Midsummer Night’s Dream directly confronts the separation between reality and what one perceive s to be real. This is examined in Titania’s interactions with Nick Bottom, in the adventures of the Athenian lovers, and, most famously, in Puck’s closing monologue. It is in this way that Shakespeare forces us to think: â€Å"What is reality?† If anything shows how perception and reality can sometimes fail to coincide it is the situation between Titania and Nick Bottom. The reality of the situation is that Nick wasn’t a highly attractive man to begin with, and has now been given an ass’ head. Titania has been drugged to believe that she is madly in love with this man, under Oberon’s orders. Here is the tricky question hidden in this situation: â€Å"What is love?† Love is a feeling. Feelings are another type of perception, a type that are impossible to ground in physical reality. One cannot say that Titania’s love is fake, though it may be. The very flower used to fill the fairy queen with this love was supposed to have been hit with one of Cupid’s arrow, the arrows which cause true love. It cannot be argued that the love is not true, but it is not of her free will. Does this make the love unreal? Surely Titania perceives it to be real but what makes love or any emotion truly real? This situation also does a good deal to show how one’s perception of reality can be altered by a powerful feeling like love. Titania is suddenly completely in love with him, with his  body, his voice, and everything. Surely she would not normally be attracted to these features but it can be almost universally agreed upon that love can alter one’s perception of things. Nick Bottom himself said that†reason and love keep little company.† Given the knowledge that something like emotion can alter one’s perception, who can say that reality is truly real? The Athenian’s love situations show that they had little grasp of reality to begin with, making them all the more susceptible toward the meddling of the fairies, which is a true test of reality versus per ception. They claim to be each equal to each other in looks, personality and strength. Even their names, Helena and Hermia are quite similar. They are nearly indistinguishable in character and mannerisms and for good reason. It is to show how powerfully love can alter the perception of a person. For Hermia, there can be no comparison between Lysander and Demetrius. This is all mixed up when the fairies become involved. Hermia, previously loved by both men, suddenly finds herself scorned and ignored. Likewise, Helena, previously ignored by both men suddenly becomes the supreme object of their desire. What is worse is that she perceives this to be nothing but a cruel joke. All of this is caused by the same flower-struck by cupid’s arrow-that had equally altered Titania’s thoughts on Nick Bottom. This begs to question, are feelings caused by substances real? There are feelings of happiness, euphoria, relaxation, and any number of things that can be caused by mind altering drugs but can these feelings be described as being real? Some would argue not, but is the argument truly that simple? What are feelings when boiled down to a science? They are no more than chemical reactions in the mind. Also, what about mood stabilizing drugs given to those depressed or suffering from bipolar disorder? Are the new feelings of well being and peace also not real? The effect of the flower is similar. Who can say how much of what is felt and what is real and how much is brought out by the flower? What of the sentiments that were brought to light by the fairy’s influence? The feelings of jealousy and distrust that were brought up in Helena were quite obviously always somewhat present so are these feelings unreal or merely highlighted by the actions of the fairies? These are all a matter of perception versus reality-something that Shakespeare clearly wanted us to think about. The final and most blunt question on reality is of course, the ending speech by Puck. â€Å"If we shadows  have offended, think but this, and all is mended, that you have but slumbered here while these visions did appear. And this weak and idle theme, no more yielding than a dream.† To start there is calling the actors all shadows, something that questions how real they truly are. Not only are they playing roles and pretending to be other people, but on top of that, how real are they or anyone really? â€Å"Think but this and all is mended† simply brings to light how easy it is to alter one’s perception of things. It’s as simple as changing how you want to see things. Then there is the big question, what is the difference between reality and a dream? If one’s perceptions are so easily changed, what is the difference between dreaming and reality? Shakespeare was a master of writing. It is the goal of any artist to change how a person feels and views things. Shakespeare takes his readers and watchers a step further by questioning feelings and perception altogether. In showing how love can so powerfully alter perceptions in Titania and Nick’s events, by showing how frequently changing the sentiments of the Athenians were, and by openly questioning how real reality is in Puck’s speech, Shakespeare challenges us to question how much of what people see and feel is real. How much of what people see and feel can simply be written off as a â€Å"Midsummer Night’s Dream.†

Historical Discoveries Of Dna And Genetic Material

When most people think of DNA, scientists, laboratories, and twisted ladders come to mind. In reality, DNA makes up genetic material, which makes up proteins that form much of the body and perform vital tasks. The study of DNA and genetic material is something more people should be aware of. As a society, knowing how powerful genetic research and technology are holds the possibility to help, or possibly hurt, people now and in the future. The study of deoxyribonucleic acid, better known as DNA, sounds modern, but in reality has been around for over 150 years. In 1856, Gregor Mendel performed his famous pea plant experiment. This experiment helped determine dominant and recessive traits. Mendel’s work faded for more than 30 years. Based on his research, Reginald Punnett developed Punnett Squares. Punnett Squares predict which traits offspring will inherit based on their parents. In 1885, scientists found chromosomes in cells. Even though there were many contributing factors, one of the most important discoveries about DNA was made by Francis Crick and James Watson. Francis Crick was born in 1916, in Northampton, England. Early in his life, he studied physics but later turned to biology. He attended University in London and earned his Ph.D in molecular biology in 1954. James Watson was born April 26, 1928, in Chicago, Illinois. He enrolled in the University of Chicago when he was just 15 years old. He earned his Ph.D. when he was 22 by completing studies on bacteriophages.Show MoreRelatedHistorical Discoveries Of Dna And Genetic Material1364 Words   |  6 Pagespeople think of DNA, scientists, laboratories, and twisted ladders come to mind. In reality, DNA makes up genetic material, which makes up proteins that form much of the body and perform vital tasks. The study of DNA and genetic material is something more people should be aware of. 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