Questions tagged [databases]

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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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16 views

Insert operation for two tables in Relational Algebra

The given schema is: Publisher(pid, name, location) Book(bid, title, author, page, price) Publish(bid, pid, publish_date) The RA question/query is: Insert new ...
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1answer
24 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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19 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
28 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
19 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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40 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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23 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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1answer
31 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
36 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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22 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
63 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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21 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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25 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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10 views

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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37 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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1answer
18 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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11 views

Anthology of term indexing

I'm interested in finding the most appropriate analogy of a data structure to describe organization/access of genetic information in cells. We humans have 23 pairs of chromosomes - each pair ...
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31 views

How does 2PL protocol apply to schedule of multiple transactions?

If a schedule follows the two-phase locking protocol, does every transaction have to follow 2PL, or is it the case that all locks must appear all unlocks in the whole schedule? I am a little confused ...
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1answer
52 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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0answers
21 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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52 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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31 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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15 views

Why is Read(Q) timestamp is not checked when a transaction issues a command reading Q?

Consider a concurrent schedule of two transactions $T_1,T_2$: $R_x(Q): T_x$ Reads $Q$ $W_x(Q): T_x$ Writes $Q$ $S:R_2(A),R_1(A),W_1(A),W_2(A)$, this schedule is not conflict serializable.However, if ...
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1answer
36 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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1answer
17 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
143 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
88 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
49 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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1answer
55 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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2answers
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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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19 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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19 views

How to create a database of meta-model transformations with real data?

I am currently working on meta-model transformation and the coevolution of models. I have already done some kind of a state of the art, and the next step in my research would be to collect some (...
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1answer
29 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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19 views

Serializable schedules but not view serializable

I know that to check if a given schedule is serializable we can test for either view serializability or conflict serializability. But do serializable schedules exist which are not view serializable?
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1answer
67 views

Need help understanding the tuple relational calculus

We say that a query in a TRC is a statement of the form $\{T: P(T)\}$, where $T$ is a tuple variable and $P(T)$ is a formula. Now my question is, what are the possible tuples $T$ to be tested i.e., ...
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22 views

Number of tables required to decompose a function into BCNF

I know this is not a question answer posting site, but for sake of explaining my doubt I will like to post a question Say you are given table like R(A,B,C,D,E,F)= {AB→C, BC → A, AC→ B , B → D , D→...
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1answer
38 views

Third Normal Form and Boyce Code normal form

I know that this is not a question answer site but for sake of explaining my doubt I have to post the entire question.. Consider the following statements. ...
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104 views

Using relational algebra to express all with a condition

I encountered this question while revising for my finals exam on database theory. The following database contains information about car repair workshops. The following tables are used: $$Workshop(\...
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1answer
106 views

Database Theory - Does the dependency preservation and lossless join properties hold for every decomposition of a relation into 3NF?

I was reading Database Systems, 6th ed by Ramez Elmasri and Shamkant Navathe. In the textbook they make a claim (in Chapter 15, section 15.2 Properties of Relational Decompositions) which I quote ...
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1answer
137 views

DBMS: MINIMUM NUMBER OF TABLES REQUIRED TO REALIZE THIS ER MODEL

I was following a discussion on a forum where they have posted a question like this--> Some people are saying that we can merge A,B,C in a single table and m:n relation of A and C in another table ...
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1answer
222 views

Does basic 2 PL always ensure conflict serializability?

While going through the DBMS book by Korth, it was mentioned : " For a set of transactions, there may be conflict-serializable schedules that cannot be obtained through the two-phase locking ...
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45 views

How to decide if two conjunctive queries cannot have any result in common

Consider the following queries: Q1: age > 18 & age < 24 & gender = 'male' Q2: age > 25 & gender = 'male' & major = 'CS' Q3: age = 20 & major = 'CS' Clearly, given any ...
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87 views

Prime attribute dependant on another prime attribute allowed under BCNF?

I have been studying DBMS ans I have a question that I got conflicting answers to: Is prime attribute that is dependant on another prime attribute allowed under BCNF? Meaning P->P. I know that NP->P ...
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539 views

Join with Bloom-filters

can you tell me how i can use a bloom-filter by a joining operation with two tables? let's assume that: Table A ={A_id,B_id,age}, Table B = {B_id, color}. now i want to use a bloom-filter so i can ...
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How do i solve this task about the the Reservoir Sampling algorithm?

Hello I have the following task (no homework). You are using the Reservoir Sampling algorithm. You process the 2000th element in the data stream and are maintaining a sample of size 500. What is ...
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In a DBMS what are the implementation details that make set operations faster than cursors?

What are the low level implementation details that make set based operations exponentially faster than iterative processes, like cursors? At a memory level how does a set operation "touch" the data ...