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The concept of functional dependency (also known as normalization was introduced by professor Codd in 1970 when he defined the first three normal forms (first, second and third normal forms). Normalization is used to avoid or eliminate the three types of anomalies (insertion, deletion and update anomalies) which a database may suffer from. These concepts will be clarified soon, but first let us define the first three normal forms. First Normal Form: A relation is in first normal form if all its attributes are simple. In other words, none of the attributes of the relation is a relation. Notice that relation means 2-diemenatioanl table. Example -1. Assume the following relation Student-courses (Sid:pk, Sname, Phone, Courses-taken) Where attribute Sid is the primary key, Sname is student name, Phone is student's phone number and Courses-taken is a table contains course-id, course-description, credit hours and grade for each course taken by the student. More precise definition of table Course-taken is : Course-taken (Course-id:pk, Course-description, Credit-hours, Grade) According to the definition of first normal form relation Student-courses is not in first normal form because one of its attribute Courses-taken is itself a table and is not a simple attribute. To clarify it more assume the above tables contain the data as shown below: Student-courses Sid Sname Phone Courses-taken 100 John 487 2454 St-100-courses-taken 200 Smith 671 8120 St-200-courses-taken 300 Russell 871 2356 St-300-courses-taken St-100-Course-taken Course-id Course-description Credit-hours Grade IS380 Database Concepts 3 A IS416 Unix Operating System 3 B St-200-Course-taken Course-id Course-description Credit-hours Grade IS380 Database Concepts 3 B IS416 Unix Operating System 3 B IS420 Data Net Work 3 C St-300-Course-taken Course-id Course-description Credit-hours Grade IS417 System Analysis 3 A Definition of the three types of anomalies: Insertion anomaly means that that some data can not be inserted in the database. For example we can not add a new course to the database of example-1,unless we insert a student who has taken that course. Update anomaly means we have data redundancy in the database and to make any modification we have to change all copies of the redundant data or else the database will contain incorrect data. For example in our database we have the Course description "Database Concepts" for IS380 appears in both St-100-Course-taken and St-200-Course-takentables. To change its description to "New Database Concepts" we have to change it in all places. Indeed one of the purposes of normalization is to eliminate data redundancy in the database. Deletion anomaly meansdeleting some data cause other information to be lost. For example if student Russell is deleted from St-100-Course-taken table we also lose the information that we had a course call IS417 with description System Analysis. Thus Student-courses table suffers from all the three anomalies. To convert the above structure to first normal form relations, all non-simple attributes must be removed or converted to simple attribute. To do that a new relation is created by combining each row of Student-courses with all rows of its corresponding course table that was taken by that specific student. Following is Student-courses table in first normal form. Student-courses ( Sid:pk1, Sname, Phone, Course-id:pk2, Course-description, Credit-hours, Grade) Notice that the primary key of this table is a composite key made up of two parts; Sid and Course-id. Note that pk1 following an attribute indicates that the attribute is the first part of the primary key and pk2 indicates that the attribute is the second part of the primary key. Student-courses Sid Sname Phone Course-id Course-description Credit-hours Grade 100 John 487 2454 IS380 Database Concepts 3 A 100 John 487 2454 IS416 Unix Operating System 3 B 200 Smith 671 8120 IS380 Database Concepts 3 B 200 Smith 671 8120 IS416 Unix Operating System 3 B 200 Smith 671 8120 IS420 Data Net Work 3 C 300 Russell 871 2356 IS417 System Analysis 3 A Examination of the above Student-courses relation reveals that Sid does not uniquely identify a row (tuple) in the relation hence cannot be the primary key. For the same reason Course-id cannot be the primary key. However the combination of Sid and Course-id uniquely identifies a row in Student-courses, Therefore (Sid, Course-id) is the primary key of the above relation. The primary key determines every attribute. For example if you know both Sid and Course-id for any student you will be able to retrieve Sname, Phone, Course-description, Credit-hours and Grade, because these attributes are dependent on the primary key. Figure 1 below is the graphical representation of the functional dependency between the primary key and attributes of the above relation.
Note that the attribute to the right of the arrow is functionally dependent on the attribute in the left of the arrow. Thus the combination (Sid, Course-id) is the determinant (that determines other attributes) and attributes Sname, Phone, Course-description, Credit-hours and Grade are dependent attributes. Formally speaking a determinant is an attribute or a group of attributes determine the value of other attributes. In addition to the (Sid, Course-id) there are two other determinants in the above Student-courses relation. These are; Sid and Course-id attributes. Note that Sid alone determines both Sname and Phone, and attribute Course-id alone determines both Credit-hours and Course_description attributes. = = Attribute Grade is fully functionally dependent on the primary key (Sid, Course-id) because both parts of the primary keys are needed to determine Grade. On the other hand both Sname,and Phone attributes are not fully functionally dependent on the primary key, because only a part of the primary key namely Sid is needed to determine both Sname and Phone. Also attributes Credit-hours and Course-Description are not fully functionally dependenton the primary key because only Course-id is needed to determine their values. The new relation Student-courses still suffers from all three anomalies for the following reasons: 1. The relation contains redundant data (Note Database_Concepts as the course description for IS380 appears in more than one place). 2. The relation contains information about two entities Student and course. Following is the detail description of the anomalies that relation Student-courses suffers from. 1. Insertion anomaly: We cannot add a new course such as IS247 with course description programming techniques to the database unless we add a student who to take the course. 2. Update anomaly: If we change the course description for IS380 from Database Concepts to New_Database_Concepts we have to make changes in more than one place or else the database will be inconsistent. In other words in some places the course description will be New_Database_Concepts and in any place were we forgot to make the changes the description still will be Database_Concepts. 3. Deletion anomaly: If student Russell is deleted from the database we also loose information that we had on course IS417 with description System_Analysis. The above discussion indicates that having a single table Student-courses for our database causing problems (anomalies). Therefore we break the table to smaller table to get a higher normal form relation. Before doing that let us define the second normal form. Second normal relation: A first normal form relation is in second normal form if all its non-primary attributes are fully functionally dependent on the primary key. Note that primary attributes are those attributes, which are parts of the primary key, and non-primary attributes do not participate in the primary key. In Student-coursesrelation both Sid and Course-id are primary attributes because they are components of the primary key. However attributes Sname, Phone, Course-description, Credit-hours and Grade all are non primary attributes because non of them is a component of the primary key. To convert Student-courses to second normal relations we have to make all non-primary attributes to be fully functionally dependent on the primary key. To do that we need to project (that is we break it down to two or more relations) Student-courses table into two or more tables. However projections may cause problems. To avoid such problems it is important to keep attributes, which are dependent on each other in the same table, when a relation is projected to smaller relations. Following this principle and examination of Figure-1 indicate that we should divide Student-courses relation into following three relations: PROJECT Student-courses ON (Sid, Sname, Phone) creates a table call it Student. The relation Student will be Student (Sid:pk, Sname, Phone) and PROJECT Student-courses ON (Sid, Course-id, Grade) creates a table call it Student-grade. The relation Student-grade will be Student-grade(Sid:pk1:fk:Student, Course-id::pk2:fk:Courses, Grade) and Projects Student-courses ON (Course-id, Course-Description, Credit-hours) create a table call it Courses. Following are these three relations and their contents: Student (Sid:pk, Sname, Phone) Sid Sname Phone 100 John 487 2454 200 Smith 671 8120 300 Russell 871 2356 Courses (Course-id::pk, Course-Description) Course-id Course-description Credit-hours IS380 Database Concepts 3 IS416 Unix Operating System 3 IS420 Data Net Work 3 IS417 System Analysis 3 Student-grade (Sid:pk1:fk:Student, Course-id::pk2:fk:Courses, Grade) Sid Course-id Grade 100 IS380 A 100 IS416 B 200 IS380 B 200 IS416 B 200 IS420 C 300 IS417 A All these three relations are in second normal form. Examination of these relations shows that we have eliminated the redundancy in the database. Now relation Studentcontains information only related to the entity student, relation Courses contains information related to entity Courses only, and the relation Student-grade contains information related to the relationship between these two entity. Further these three sets are free from all anomalies. Let us clarify this in more detail. Insertion anomaly: Now a new Course with course-id IS247 and Course-description can be inserted to the table Course. Equally we can add any new students to the database by adding their id, name and phone to Student table. Therefore our database, which made up of these three tables does not suffer from insertion anomaly. Update anomaly: Since redundancy of the data was eliminated no update anomaly can occur. To change the course-description for IS380 only one change is needed in table Courses. Deletion anomaly: the deletion of student Russell from the database is achieved by deleting Russell's records from both Student and Student-grade relations and this does not have any side effect because the course IS417 untouched in the table Courses.
Third Normal Form: A second normal form relation is in third normal form if all non-primary attributes (that is attributes that are not parts of the primary key or of any candidate key) have non-transitivity dependency on the primary key. Assume the relation: STUDENT (Sid: pk, Activity, fee) Further Activity ------------> fee that is the Activity determine the fee Sid Activity Fee 100 Swimming 100 200 Tennis 100 300 Golf 300 400 Swimming 100 Table STUDENT is in first normal form because all its attributes are simple. Also STUDENT is in second normal form because all its non-primary attributes are fully functionally dependent on the primary key (Sid). Notice that a first normal relation with non-composite (that is simple) primary key automatically will be in second normal form because all its non-primary attributes will be fully functionally dependent on the primary key. Table STUDENT suffers from all 3 anomalies; a new student can not be added to the database unless he/she takes an activity and no activity can be inserted into the database unless we get a student to take that activity. There is redundancy in the table (see Swimming), therefore to change the fee for Swimming we must make changes in more than one place and that will cause update anomaly problem. If student 300 is deleted from the table we also loose the fact that we had Golf activity with its fee to be 300. To overcome these anomalies STUDENT table should be converted to smaller tables. Consider the following three projection of the STUDENT relation: PROJECT STUDENT on [Sid, Activity] and we get a relation name it STUD-AVT (Sid:pk, Activity) with the following data : STUD_ACT Sid Activity 100 Swimming 200 Tennis 300 Golf 400 Swimming PROJECT STUDENT on [Activity, Fee] and we get a relation name AVT-Fee (Activity:pk, Fee) with the following data : AVT-Fee Activity Fee Swimming 100 Tennis 100 Golf 300 Swimming 100 PROJECT STUDENT on [Sid, Fee] and we get a relation name Sid-Fee (Sid:pk, Fee) with the following data : Sid-Fee Sid Fee 100 100 200 100 300 300 400 100 The question is which pairs of these projections should we choose? The answer to that is to choose the pair STUD-AVT and AVT-Fee because the join of these two projections produces the original STUDENT table. Such projections are called non-loss projections. Therefore the join of STUD-AVT and AVT-Fee on the common attribute Activity recreate the original STUDENT table. On the other hand as shown below the join of projections Sid-Fee and AVT-Fee on their common attribute Sid generates erroneous data that were not in the original STUDENT table and such projections are called loss projections. Following is the join of projections Sid-Fee and AVT-Fee on their common attribute Sid Sid Activity Fee 100 Swimming 100 100Tennis 100 200 Tennis 100 200 Swimming 100 300 Golf 300 400 Swimming 100 400 Tennis 100 The three rows marked in red color were not in the original STUDENT table. Thus we have an erroneous data in the database. Both projections STUD-AVT and AVT-Fee are in third normal form and they do not suffer from any anomalies. Boyce Codd normal (BOC): A relation is in BOC form if every determinant is a candidate key. This is an improved form of third normal form. Fourth Normal Form: A Boyce Codd normal form relation is in fourth normal form if there is no multi value dependency in the relation or there are multi value dependency but the attributes, which are multi value dependent on a specific attribute, are dependent between themselves. This is best discussed through mathematical notation. Assume the following relation R(a:pk1, b:pk2, c:pk3) Recall that a relation is in BOC normal form if all its determinant are candidate keys, in other words each determinant can be used as a primary key. Because relation R has only one determinant (a, b, c),, which is the composite primary, key and since the primary is a candidate key therefore R is in BOC normal form. Now R may or may not be in fourth normal form. 1. If R contains no multi value dependency then R will be in Fourth normal form. 2. Assume R has the following two-multi value dependencies: a ------->> b and a ---------->> c In this case R will be in the fourth normal form if b and c dependent on each other. However if b and c are independent of each otherthen R is not in fourth normal form and the relation has to be projected to following two non-loss projections. These non-loss projections will be in fourth normal form. Example:Case 1: Assume the following relation:Employee (Eid:pk1, Language:pk2, Skill:pk3) No multi value dependency, therefore R is in fourth normal form. case 2: Assume the following relation with multi-value dependency: Employee (Eid:pk1, Languages:pk2, Skills:pk3) Eid ---->> Languages Eid ------>> Skills Languages and Skills are dependent. This says an employee speak several languages and has several skills. However for each skill a specific language is used when that skill is practiced. EidLanguage Skill 100 English Teaching 100 Kurdish Politic 100 French cooking 200 English cooking 200 Arabic Singing Thus employee 100 when he/she teaches speaks English but when he cooks speaks French. This relation is in fourth normal form and does not suffer from any anomalies.
case 3: Assume the following relation with multi-value dependency: Employee (Eid:pk1, Languages:pk2, Skills:pk3) Eid ---->> Languages Eid ------>> Skills Languages and Skills are independent. EidLanguage Skill 100 English Teaching 100 Kurdish Politic 100 English politic 100 Kurdish Teaching 200 Arabic Singing This relation is not in fourth normal form and suffers from all three types of anomalies.Insertion anomaly:To insert row (200 English Cooking) we have to insert two extra rows (200 Arabic cooking), and (200 English Singing) otherwise the database will be inconsistent. Note the table will be as follow: Eid Language Skill 100 English Teaching 100 Kurdish Politic 100 English politic 100 Kurdish Teaching 200 Arabic Singing 200 English Cooking 200 Arabic Cooking 200 English Singing Deletion anomaly: If employee 100 discontinue politic skill we have to delete two rows (100 Kurdish Politic), and (100 English Politic) otherwise the database will be inconsistent.Update anomaly:If employee 200 changes his skill from singing to dancing we have to make changes in more than one place The relation is projected to the following two non-loss projections which are in forth normal form Emplyee_Language(Eid:pk1, Languages:pk2) EidLanguage 100 English 100 Kurdish 200 Arabic Emplyee_Language(Eid:pk1, Skills:pk2) EidSkill 100 Teaching 100 Politic 200 Singing
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∙ 15y ago
Dependency theory is a perspective in Social Sciences, primarily in economics, that argues developing countries are effectively dominated and exploited by developed nations through economic relationships. It posits that the global economic system is structured in a way that perpetuates underdevelopment and limits the growth potential of poorer countries. Dependency theory emphasizes the importance of understanding historical and ongoing unequal power dynamics in international economic relations.
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Where is the lowest rate of welfare dependency in the US?
According to data from the U.S. Census Bureau, New Hampshire has the lowest rate of welfare dependency in the United States. This is often attributed to the state's low unemployment rate and strong economy.
The ratio of non-working population to working age population is called?
The ratio of non-working population to working age population is called the dependency ratio. It is used to assess the pressure placed on the working population to support the dependent population.
Where is the highest rate of welfare dependency in the US?
Areas in the southern United States, such as Mississippi and New Mexico, tend to have some of the highest rates of welfare dependency in the country. These states often have higher levels of poverty and unemployment, contributing to a greater need for social assistance programs.
What is the name of the theory that Darwin developed after traveling on the HMS Beagle?
The theory that Darwin developed after traveling on the HMS Beagle is known as the theory of evolution by natural selection. It proposes that species evolve over time through processes such as natural selection, where individuals with advantageous traits are more likely to survive and reproduce.
What did Darwin's theory of evolution suggest?
Darwin's theory of evolution suggested that species evolve over time through a process called natural selection, where organisms with favorable traits are more likely to survive and reproduce. This process leads to the gradual change and adaptation of species to their environment.
What are the different between modernization theory and dependency theory?
Modernization theory focuses on how underdeveloped countries can develop and advance by adopting Western practices and technology. On the other hand, dependency theory argues that underdeveloped countries are exploited by more powerful nations, leading to their underdevelopment. Dependency theory emphasizes the negative impact of global economic structures on developing countries, while modernization theory focuses on internal factors for development.
What is the Modernization theory and the dependency theory?
The modernization theory puts the most emphasis on economic development social and cultural change, and political stability. The theory believes that certain steps can bring success to every country and that the policies and ways of western countries is best. An important difference with the dependency theory is that western countries force their rules and policies on developing countries. The dependency theory was developed to criticize the modernization theory.
How does dependency theory relate to third world societies?
Dependency theory posits that third world societies are kept in a state of underdevelopment due to their economic dependence on more developed nations. This theory argues that the exploitation of resources, unequal trade relationships, and historical colonial legacies perpetuate poverty and hinder development in these societies. Dependency theory highlights the structural disparities and power dynamics that contribute to the economic and social challenges faced by third world countries.
What do critics of dependency theory claim?
critics of dependency theory says that any nation that has stopped imports items to its country has lessen the competition and to improve work for better services which is rendered to customers.
Does dependency theory run in families genetics?
"The theory of dependency running in family genetics is an ongoing study. There is strong evidence that there is a genetic component to many dependencies therefore I would say that yes, it does run in family genetics."
What are the merits of dependecy theory?
Dependency theory highlights how power dynamics between core and periphery countries perpetuate global inequality. It sheds light on how historical exploitation, unequal exchange, and structural barriers hinder the development of peripheral countries. By emphasizing the impact of external influences, dependency theory offers a critical perspective on globalization and calls for more equitable international relations.
What is neo-colonial dependency theory?
Neo-colonial dependency theory suggests that former colonial powers maintain economic, political, and cultural control over former colonies through indirect means, such as economic policies and trade relations. It argues that this continued dependency perpetuates underdevelopment in the formerly colonized countries.
Discuss the main tenets of the dependency theory and analyze its analytical relevancy to developing countries?
Dependency theory asserts that developing countries are exploited and kept in a state of underdevelopment by the dominant developed economies through unequal trade relationships and economic dependence. It highlights the role of historical colonialism and neo-colonial practices in perpetuating this dependence. Dependency theory remains relevant in analyzing the challenges faced by developing countries in achieving economic independence and sustainable development in the globalized world economy.
What are the Weakness of dependency theory of development in Africa?
Some weaknesses of dependency theory in the context of African development include its tendency to oversimplify complex issues, its focus on external factors at the expense of internal dynamics, and its potential to perpetuate a victim mentality among developing countries. Additionally, the theory has been criticized for being deterministic and not providing a clear path for how countries can break free from dependency relationships.
What are the main arguments of the dependency theory its causes and solutions of underdevelopment in third world countries?
Dependency theory argues that underdevelopment in third world countries is a result of the unequal economic relations between developed and underdeveloped nations, with the latter being dependent on the former. This dependency is perpetuated by factors such as neocolonialism, exploitation of resources, and unequal trade relationships. Solutions proposed by dependency theory include promoting self-sufficiency, reducing reliance on foreign investment, and fostering economic policies that prioritize domestic development.
What are the characteristics of dependency theory?
Dependency theory suggests that global inequality is largely due to the exploitation of developing countries by developed countries. It emphasizes the role of historical colonialism and neocolonial practices in perpetuating underdevelopment. Dependency theorists argue that developing countries are structurally dependent on developed countries for resources, technology, and markets, leading to unequal power relations.
How applicable is dependency theory?
Dependency theory can be applicable in analyzing the unequal power dynamics between developed and developing nations, especially in terms of economic exploitation and political influence. It emphasizes the role of external factors in shaping the development trajectory of countries. However, dependency theory has been criticized for oversimplifying complex issues and not accounting for internal dynamics within nations. Its applicability may vary depending on the specific context being analyzed.
