Questions tagged [databases]
The databases tag has no usage guidance.
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Need Clarification on Storage Media Statements - Seeking Help
I am currently working on a set of questions related to storage media, and I've come across a statement that seems a bit confusing to me. The question is as follows:
Mark all correct statements ...
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This diagram serves to determine the components of a data entry in my database. What is the name of this type of diagram?
To properly insert a data entry in my database, I have to reach the last box in this diagram. A box represents either a flag or a data structure that participates in determining a single entry. What ...
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Polynomial time algorithm for solving SQL queries with EXISTS and NOT EXISTS subqueries
Let $Q$ be a query in the fragment of SQL built up from basic $SELECT$ clauses using
subqueries with $EXISTS$ and $NOT EXISTS$. Then for each such fixed query $Q$ I'm trying to show that there is a ...
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Is there an algorithm for finding rows that have same sum of column values up to a threshold value?
I have a table like this (more specifically a nested dictionary)
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Real world example of complex foregin key references
Give a real world, normalized example where table T1 has primary key (A, B), T2 has primary key (B, C) and T3 has primary key (A, C) and table 4 has a primary key (A, B, C) where (A,B) is a foregin ...
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Practical applications of finite model theory to databases
I have heard that finite model theory has connections to database theory. Is there an example of where this database theory could be used by programmers developing database applications?
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Is there a sorting program or formula to sort and place individuals in classes based on preferences
I am looking for a formula or program to help place people in classes based on their preferences.
The elements of the problem are:
There are 30 class choices a student can pick from.
There are 400 ...
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39
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What is Triangular bottom database?
For algorithm design course, the teacher gave a question, but i don't understand it at all, specially the triangular bottom database which i searched about it but couldn't find any result. However the ...
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Trying to figure out how to model the structure of a multilingual dictionary for several constructed languages (basically Wiktionary for my conlangs)
Okay, so, this will be quite a bit, sorry. I'm working on several constructed languages for a worldbuilding project. Up until this point, I have been using a spreadsheet to store the vocab; each row ...
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Check whether a decomposition is in 3nf
In a database systems course, we have been presented with the following definition for third normal form (3NF):
A relation $R$ is in 3NF means:
a nontrivial dependency $A_1,\dots,A_n\to B_1,\dots B_m$...
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Relational calculus: "Find all X with at least y amount of Z"
Assuming I have two relations:
Supplier [ID (PK), Name, City, Country] and
Item [ID (PK), Name, Department, Price, Stock, Supplier_ID (FK)]
What would be the easiest way to determine the following ...
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Implement this as Attribute or Entity Set?
I am creating a database on students' interests using the Entity-Relationship Model for a University assignment.
Should I implement the circled stuff as attribute, or an entity set?
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How can we reduce the spatial complexity of intermediate indexes in relational databases at execution time?
In relational databases, what are the practical or theoretical ways to reduce the size and spatial complexity of intermediate indexes or tables* at execution time (so for example to reduce the size of ...
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Algorithm to generate unique suggestions for creating an ID
Let's say I have a service where I provide user registration. The user chooses a ID. Now if I already have someone who is registered against that ID, I will inform the user that this ID is already ...
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Primary key's all field should contain value or not?
After reading a lot of materials related to the Primary key and Unique key, I am in doubt. Let us consider a primary key (AB) in table R (ABCDE). AB together can not be null as AB is a primary key. ...
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Is this decomposition in 3NF?
I have the following question:
Consider relation R(A, B, C, D, E, F, H) with the following functional dependencies:
A --> D, AE --> H, DF --> BC, E --> C, H --> E
Consider three ...
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Primary File Organization in DBMS - Files of ordered records (sorted files)
"Fundamental of Database Systems", 3rd ed. by Elmasri and Navathe, page 136 says:
"We can physically order the records of a file on disk based on the values of one of their fields [...]&...
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Mongodb database model for password manager app
I'm doing a school project where I have to design a password manager app. I was wondering what the data model would look like. I know that I will have the user database to store authentication ...
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How are data structures used along databases?
I just completed a Data structures and Algorithms course in my university. I know how data structures work and how different DS are used to solve specific and to improve efficiency. I have also ...
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Advantages to create Male and Female entities separate from User rather than making gender a property in a database?
The screenshot is from Georgia Tech's CS-6400. The instructor was talking about inheritance of Sub-Types and Super-Types.
My question is, why are Male and ...
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Efficient data structure supporting search query with contains
Suppose I have a table with millions strings in it as keys.
What data structure can I use in order to efficiently support only queries like that?
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What does it mean to 'provide' an API call?
So I have a database pre-loaded with data related to food recipes and the assignment says:
'Provide an API call that allows us to specify an ingredient or set of ingredients and return full recipes ...
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Automated Query Equivalence Solver (MongoDB)
The query-equivalence problem is undecidable. However there are theorem provers that attempt to solve instances of undecidable problems. I am curious how I could go about using an automatic theorem ...
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347
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AVL Tree rotations
What size is the largest AVL tree for which an insertion could trigger a double rotation?
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154
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Figuring out the equivalence between two definitions of "transitive functional dependencies" and intuition behind the intended meaning of definition
The definition given below is present in the exercise of the text Database System Concepts by Korth et. al.
Let $\alpha$ and $\beta$ be sets of attributes such that $\alpha \rightarrow \beta$ holds, ...
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Is this a mistake in the textbook? Fundamentals of Database Systems 7th ed
Aggregation is an abstraction concept for building composite objects from their
component objects. ... the possibility of combining objects
that are related by a particular relationship instance into ...
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where to get detailed information about some file format?
i want to learn about the structure of a .blk file but the problem is I don't know where to look for detailed information of this sort, most of the google searches I made gave me links to viewers.
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Creating a database of math questions and of answers and a front end for them
Need some guidance on where to begin. I am just learning python if it has any bearing.
I want to create a page on my site where users log in, choose multiple topics from a list, choose between levels ...
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How to simplify the query qualification?
Given the following DB and query :
Now if we need to simplify the query qualification, here is the answer from the book (Principle of distributed database systems, third edition) :
My question is in ...
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First normal form
I am confused about an aspect of the definition of first normal form in relational database model.
Codd 1970 ("A Relational Model of Data for Large Shared Data Banks") defines normalization (...
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constant relation in the base case of relational algebra
in the base case of the inductive definition of the operations of the relational algebra there is also the so called "constant relation" (as for example found in the definition here https://...
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What is meant by A determine BC in functional dependency. How the validity of this statement will be checked
We use notation A determines BC in a database for functional dependency. Same way we use equations in mathematics which shows dependency of variables. We have inference rules in logics, functions in ...
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In database buffering why is it important : no writes to a block (which is to be moved from the disk buffer section of main memory) be in progress?
I was going through the concept of database buffering from the Database System Concepts text by Korth et. al where I came across the excerpt below.
The rules for the output of log records limit the ...
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WAL rule requires only the undo information in the log have been output to stable storage, and permits the redo information to be written later
I was going through the "write-ahead logging (WAL) rule" from the Database System Concepts text by Korth et. al, where I came across the following excerpt:
Strictly speaking, the WAL rule ...
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Is there computer for specify purpose that perform database task?
Is database server really really exist? i mean the server wasn't made by general purpose computer but that database device have their own hardware and architecture.
We know that good database server ...
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Algorithm to calculate the period where cumulative days within a rolling period exceeds a threshold
I'm struggling to think of the algorithm to transform one data set to another.
The problem I'm looking at is creating a dataset of periods of time where cumulative days absent within a period (eg 30 ...
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Which of the query approaches are more efficient?
There are two relations, registered(participant,topic) and fee(participant,amount).
The primary key for registered is (participant, topic) and the primary key for fee is participant.
The premise is ...
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Data model and database schema
I need to test my understanding of the difference between the data model and database schema. According to my understanding, the data model is a description of how the data will be stored and the ...
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Database Access Cost Estimate - Linear Search over non-key attribute
How does one estimate the access cost for the below query given that the data is sorted according to a non-key attribute, that the data is not uniformly distributed across all possible values of said ...
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What is the difference between a state machine and a database
I didn't study computer science as a degree, so whilst having studied computer science, there are still gaps in my knowledge. Everything I read about 'state' sounds like some form of 'data' but kept ...
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If a user confirmed a booking or transaction on the database system, but it failed and it falls over to the replica, what if the transaction is lost?
This is an overall system design and DBMS question:
If the user books a ticket or an item on a website, how do we solve the issue of confirming a ticket is sold to the user, but the main Database ...
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How attributes helps us to allow column interchange in a relational database?
A relation on two sets $A$ and $B$ is defined as the subset of the cartesian product $$A\times B = \{(a,b),\ a \in A, b \in B\}$$
A database is also a relation and each entry is an ordered tuple ...
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Is Neo4J computationally equivalent to relational algebra
I am wondering whether Neo4j and the associated Cypher query language is computationally equivalent to relational algebra?
Any ideas or papers on that topic?
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Relation is in 2NF or not?
Consider a relation R(A,B,C,D,E) and the only FDs,
ABD->C
BC->D
CD->E
These are the only 3 FDs. I want to know if the above relation is in 2NF or not.
According to the definition of 2NF, a ...
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Resources about implementing a database table
I'd like to understand more how data can be stored on disk so it can be read quickly. I don't want to say database record because I'm not asking how to build a database. My question is closer to how ...
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Find number of candidate keys given non-trivial functional dependency X->Y, where X is some set of attributes and Y is some prime attribute
In a relation R, if X is some set of attributes and Y is some prime attribute such that X uniquely determines Y is a non-trivial FD. Then is it true that R has at least two candidate keys?
For ...
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External Sorting - Calculate passes with different number of disks
Let suppose that we have a file with n = 10^6 records. The block size is B = 10 records and we have available main memory m = 20 blocks. (Sorting with MergeSort)
a) If we have 1 disk find minimum ...
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Is persistence a property of a database?
I was having a discussion in another forum on this topic, and I couldn’t get a satisfactory answer. Originally, a statement was made that a redis data store couldn’t be considered a database because ...
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Does upgrading after all locks and before all unlocks violate 2PL?
2PL's rule says:
Upgrading of lock (from S(a) to X (a)) is allowed in growing phase.
But what if upgrading lies after the last lock and before the first unlock? Does it still count "in the ...
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What does mean by the independent columns in 4NF normalization?
For a table to satisfy the Fourth Normal Form, it should satisfy the following two conditions:
It should be in the Boyce-Codd Normal Form.
And, the table should not have any Multi-valued Dependency.
...
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