Questions tagged [databases]
The databases tag has no usage guidance.
213
questions
0
votes
0
answers
19
views
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 ...
- 1
0
votes
0
answers
38
views
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 ...
- 111
0
votes
0
answers
13
views
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 ...
- 1
0
votes
1
answer
27
views
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 $A_1,\dots,A_n\to B_1,\dots B_m$...
1
vote
0
answers
28
views
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 ...
- 11
0
votes
0
answers
23
views
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?
2
votes
0
answers
28
views
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 ...
- 21
0
votes
0
answers
141
views
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 ...
- 769
0
votes
0
answers
19
views
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. ...
- 168
0
votes
0
answers
50
views
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 ...
2
votes
0
answers
33
views
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 [...]&...
- 21
0
votes
0
answers
27
views
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 ...
- 1
0
votes
1
answer
131
views
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 ...
- 25
1
vote
0
answers
32
views
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 ...
- 13
0
votes
0
answers
80
views
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?
...
- 101
0
votes
1
answer
17
views
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 ...
3
votes
1
answer
74
views
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 ...
- 31
0
votes
1
answer
285
views
AVL Tree rotations
What size is the largest AVL tree for which an insertion could trigger a double rotation?
- 11
0
votes
1
answer
102
views
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, ...
- 1,042
1
vote
1
answer
66
views
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 ...
0
votes
0
answers
17
views
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.
- 1
0
votes
0
answers
175
views
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 ...
- 1
2
votes
1
answer
26
views
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 ...
- 23
1
vote
0
answers
22
views
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 (...
- 121
1
vote
0
answers
52
views
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://...
- 155
0
votes
0
answers
53
views
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 ...
0
votes
1
answer
64
views
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 ...
- 1,042
0
votes
1
answer
108
views
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 ...
- 1,042
-1
votes
1
answer
24
views
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 ...
0
votes
1
answer
42
views
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 ...
1
vote
0
answers
37
views
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 ...
1
vote
1
answer
48
views
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 ...
- 21
2
votes
0
answers
71
views
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 ...
- 123
0
votes
1
answer
309
views
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 ...
- 101
2
votes
2
answers
46
views
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 ...
0
votes
0
answers
56
views
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 ...
- 33
1
vote
0
answers
31
views
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?
- 91
0
votes
1
answer
310
views
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 ...
- 11
1
vote
1
answer
50
views
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 ...
- 113
0
votes
1
answer
405
views
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 ...
- 147
0
votes
0
answers
51
views
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 ...
- 19
0
votes
1
answer
37
views
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 ...
- 101
1
vote
1
answer
537
views
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 ...
- 13
1
vote
0
answers
56
views
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.
...
- 168
0
votes
2
answers
155
views
Example for Database architecture
PHPMyadmin is stated as a 3 tier database architecture.How is this possible,Isn't it a 2 tier architecture.What are the real world examples of 1-tier and 2-tier architecture.
- 11
1
vote
0
answers
68
views
In index allocation scheme, what parameters does the maximum size of a file depends on?
My understanding is as follows:
...
- 11
1
vote
0
answers
42
views
What does the three schema architecture of DBMS refer to?
This architecture contains three layers or levels of the database management system:
External level
Conceptual level
Internal level
Can some one explain to me with a practical real example so that ...
- 11
0
votes
2
answers
168
views
how two phase commit ensure serializability
Two phase commit is used in distributed transaction. For example, a client sends a transaction to two databases with a coordinator.
step1: client get a global transaction id from coordinator
step2: ...
- 101
0
votes
1
answer
27
views
Bits needed to send parameters of perfect hash functions
Suppose that there is a server that has $n$ files. The server is used to construct a perfect hash function for those files and then the computed parameters will be sent to a user. These parameters ...
- 123
2
votes
1
answer
586
views
Efficiently storing and modifying a reorderable data structure in a database
I'm trying to create a list curation web app. One thing that's important to me is being able to drag-and-drop reorder items in the list easily. At first I thought I could just store the order of each ...
- 21