Mapping Objects to Relational Databases: O/R Mapping In Detail
is to present a complete taxonomy of recursive relationships with their differ ence to correct an error in the early phases as opposed to the post- implementation. Recursive. Relationships. One of the more difficult—and often important— relationship types to implement is the recursive relationship, also known as a self -join. Physical data model includes all required tables, columns, relationship, database properties for the physical implementation of databases.
Or using what the. NET folks have coined as a "code first" approach to database design. The first thing to note is that a Python class named Employee is being declared, which inherits from the django. This inheritance gives the Employee class the functionality to access the database through Django's ORM.
These are sort of like enums which specify the different roles an employee can assume. In fact, the tuple of tuples constant is passed to the definition of the roles class field to signify what values the class should be allowed to accept.
The final field being defined is perhaps the most meaningful one, the manager field. It is a foreign key that defines a recursive relationship between employees and their managers. This means that the implicit auto incrementing integer id column that Django makes on models that inherits from django.
Model will be available as a foreign key value for the same class or table. This will satisfy our use-case which could be stated as, "an employee may only have one direct manager or no manager in the case of the president, but an employee may manage many different employees". By specifying self as the first parameter of the model. ForeignKey call, Django will set this up as a recursive relationship.
Below is a ERD diagram of the recursive relationship we have defined. In the command line, within a our virtual environment of course, run the following to create the default tables which all Django apps utilize.
By default, this database is a sqlite database within the root project folder.
Do this by issuing the following commands and make sure you observe the output as shown below: Jane Doe is the president.
Then John Doe has a manager role and is managed by his mother Jane Doe yes, there is clearly some nepotism here.
We can test our relationship field of employee by inspecting the output of calling employee on our johnD variable: It looks like things are working as expected. Setting Up Our View In the same directory as our "hrmgmt" directory make another directory called "templates". Then within the "templates" directory make yet another directory called "hrmgmt". It is within this file that we will write the code to build out our listing of employees. Copy and paste in the following code: Templates represent a blueprint for reproducible HTML that is dynamically generated based off the data that is passed to it.
Write a program to produce each of the following recursive patterns. The ratio of the sizes of the squares is 2. To draw a shaded square, draw a filled gray square, then an unfilled black square.
Animated towers of Hanoi animation. Write a program AnimatedHanoi. Consider the following recursive function in Collatz. The unsolved problem is that no one knows whether the function terminates for all integers mathematical induction is no help because one of the recursive calls is for a larger value of the argument.
Mandelbrot asked the famous question How long is the coast of Britain? The modifications are simple: Experiment with various values of the arguments to get your program to produce islands with a realistic look.
Write a recursive program PlasmaCloud. Consider McCarthy's 91 function: Give the number of recursive calls used by mcCarthy to compute this result.
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Prove that the base case is reached for all positive integers n or find a value of n for which this function goes into a recursive loop. Write a program Tree. Web Exercises Does Euclid. If not, fix it. When calling the function, take the absolute value of both inputs.
Write a recursive program GoldenRatio. Discover a connection between the golden ratio and Fibonacci numbers. What is mystery 1, 7?
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Give a high level description of what mystery a, b returns, given integers a and b between 0 and Successive recursive calls reduce b by 1, driving it toward the base case. Consider the following function. What does mystery 0, 8 do?Relationship type in dbms with example - Recursive Relationships - DBMS gate lectures in hindi - #9
Repeat the previous exercise, but replace if a! Compare this to Fibonacci. Write a program that takes a command-line argument N and prints out the first N Fibonacci numbers using the following method proposed by Dijkstra: Write a program Pell. Consider the following function from program Recursion.
What would happen in the previous exercise if the base case was replaced with the following statement? Consider the following pair of mutually recursive functions. What does g g 2 evaluate to?
Transformations by increment and unfolding. Write a recursive program Hadamard. Do not use an array. A 1-by-1 Hadamard pattern is a single black square. In general a 2N-by-2N Hadamard pattern is obtained by aligning 4 copies of the N-by-N pattern in the form of a 2-by-2 grid, and then inverting the colors of all the squares in the lower right N-by-N copy.
This property makes it useful for designing error-correcting codes. Here are the first few Hadamard matrices. In this exercise, you will solve the classic 8-queens problem: Any permutation p of the integers 0 to 7 gives such a placement: It is based on program Permutations. Towers of Hanoi variant II. Knuth-Graham and Pathashnik Solve the original Towers of Hanoi problem, but with the extra restriction that you are not allowed to directly transfer a disk from A to C.
How many moves does it take to solve a problem with n disks? Towers of Hanoi variant III. Repeat the previous question but disallow both A to C and C to A moves. That is, each move must involve pole B.
Towers of Hanoi with 4 pegs. Suppose that you have a fourth peg. What is the least number of moves needed to transfer a stack of 8 disks from the leftmost peg to the rightmost peg? Finding the shortest such solution in general has remained an open problem for over a hundred years and is known as Reve's puzzle. Another tricky recursive function.
What is f 0? Write a function to check if n is a Fibonacci number. Random infix expression generator. What do you observe?
What is F ? The answer is related to the Fibonacci sequence and the Zeckendorf representation of a number. The von Neumann integer i is defined as follows: This is a method for defining ordinals in set theory. Subsequences of a string.
Write a program Subsequence.
Write a program BinaryGCD. Write a program Partition. A partition of N is a way to write N as a sum of positive integers. Two sums are considered the same if they only differ in the order of their constituent summands. Partitions arise in symmetric polynomials and group representation theory in mathematics and physics.
Write a program JohnsonTrotter. Write a program PermutationsLex. A derangement is a permutation p of the integers from 0 to N-1 such that p[i] doesn't equal i for any i.
Write a program to count the number of derangements of size N using the following recurrence: The first few terms are 0, 1, 2, 9, 44,, and The tribonacci numbers are similar to the Fibonacci numbers, except that each term is the sum of the three previous terms in the sequence.
The first few terms are 0, 0, 1, 1, 2, 4, 7, 13, 24, 44, Write a program to compute tribonacci numbers. What is the ratio successive terms?
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Sum of first n Fibonacci numbers. Print out all combination of k of n items in such a way that consecutive combinations differ in exactly one element, e. Create a maze using divide-and-conquer: Begin with a rectangular region with no walls.
Choose a random gridpoint in the rectangle and construct two perpendicular walls, dividing the square into 4 subregions. Choose 3 of the four regions at random and open a one cell hole at a random point in each of the 3. Recur until each subregion has width or height 1.
Here's an by example.
Here's a referenceincluding a simple 1D version. Doesn't have all of the statistical properties of 2D fractional Brownian motion. Write a recursive program to draw a fern or tree, as in this fern fractal demo. Use memoization to develop a program that solves the set partition problem for positive integer values.
You may use an array whose size is the sum of the input values. Banzhaf III proposed a ranking system for each coalition in a block voting system. Suppose party i control w[i] votes.