Questions tagged [databases]

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I am preparing for Bank PO and I require suggestion for buying theoritical books

I am preparing for Bank PO exams and I require some guidance about books which contain topics like MS Office, Network Systems(Star ,Bus etc.) and also computer history(generations and all). I would ...
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1answer
58 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, ...
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1answer
49 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 ...
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17 views

Are there some database models (or possibly data structures) which implement some aspects of relational algebra without using SQL?

Are there some database models (or possibly data structures) which implement some aspects of relational algebra without using SQL? More precisely, are there some RDMS which use the host language as a ...
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15 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.
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39 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 ...
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8 views

Explain how a text retrieval db & query differs from a document db and query and which do I need?

To any and all, I am in need of either a text retrieval database, a document database, a hybrid database, something custom, or perhaps something else. I am asking for someone to explain the ...
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31 views

Can a Non-Prime attribute functionally determine a Prime attribute?

In Relational Databases, Prime attributes are defined as the attributes that are a subset of any candidate key. Thus, the attributes that are not a subset of any candidate key are Non-Prime. My ...
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18 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 ...
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12 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 (...
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27 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://...
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43 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 ...
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31 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 ...
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33 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 ...
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21 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 ...
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12 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 ...
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26 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 ...
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13 views

Is it possible to reduce the cost based rule further by applying a heuristic rule?

How can the Cost-Based Approach: Linear search on a heap file that has no index Binary search on a sorted file that has no index Equality search on an attribute that has a hash index Equality search ...
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43 views

How to Concurrently Add a Row to a Relational Database

Say I have a relational database and I want to support allowing multiple writers to add create a new row in the same table. How is this implemented? I've read a lot about locks for dealing with ...
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1answer
37 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 ...
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27 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 ...
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1answer
56 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 ...
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1answer
25 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 ...
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45 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 ...
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27 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?
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74 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 ...
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1answer
39 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 ...
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31 views

Lost Update Problem and Recoverability and Commits

Does lost update problem must have Read first? Can Lost-Update problem occur in: 1] Conflict Serializable 2] Strict Recoverable I'm totally confused about basic. R2(X) R1(X) W1(X) C1 W2(X) Does this ...
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1answer
141 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 ...
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27 views

What is the state of the art of full text searching across languages?

I have looked at a few papers on this such as this, and it basically says that full text search is all about English with few resources for languages without spaces between words (like Chinese or ...
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36 views

Mathematical representation of value set of a composite attribute

Following is a paragraph on page 70 of Fundamentals of Database Systems by Ramez Elmasri: Mathematically, an attribute $A$ of entity set $E$ whose value set is $V$ can be defined as a function from $...
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Dynamic replica membership in a distributed causally-consistent database

Given a distributed causally-consistent database (a replicated key-value store where writes are propagated in causal order, in the style of this paper), what are common techniques for "scaling&...
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39 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 ...
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16 views

Cardinality of weak relationships

I want to ask what is the cardinality of a weak relationship like the loan payment relationship shown below, will be ? I am guessing it should be many to many.
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21 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 ...
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128 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 ...
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23 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. ...
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99 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.
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In index allocation scheme, what parameters does the maximum size of a file depends on?

My understanding is as follows: ...
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34 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 ...
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1answer
49 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: ...
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18 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 ...
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1answer
272 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 ...
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1answer
93 views

Databases and B-Trees: What are Keys and how are they related

I confused about the description & definition of "key" occuring as terminology for databases and b-trees. In first case dealing with theory of databases a key is defined as a choice for ...
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1answer
56 views

What is the maximum number of indices one can create on a table with N columns?

Say, I have a database table with $N$ columns. What is the (theoretical) maximum number of indices I can create on that table? For $N = 1,2,3$ it's easy enough to calculate the answer $(1, 4, 15)$, ...
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355 views

Confused between 2 phase locking and 2 phase commit

I understand that both algorithms are very different, but what I don't understand is whether they achieve the same thing in the end. 2PC is for atomic commits and 2PL is for serializable isolation. ...
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Parsing text, then searching it: one entry per position, vs. 1 JSON column per text

I have a Rails application using Postgresql. Texts get added to the application (ranging in size -- as short as a few words, to as long as, say, 5,000 words?). The text gets parsed, both ...
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26 views

Relation Closure for F+

$A \rightarrow B C$ $C D \rightarrow E$ $B \rightarrow D$ $E \rightarrow A$ I have these Relations for R={A,B,C,D,E} Now I have to calculate the closure $F^+$ and give the candidate keys I came ...
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1answer
33 views

Incremental View Maintenance for projection

I was reading https://www2.cs.duke.edu/courses/spring02/cps296.1/lectures/08-view.pdf Or in the paper "Incremental Maintenance of Views with Duplicates," by Griffin and Libkin, SIGMOD, 1995. figure 2....

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