Questions tagged [databases]
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206
questions
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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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24 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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0answers
8 views
Need Suggestion for Level 1 Data Flow Diagram
I have created level 1 DFD for following application. I need suggestions, how can I improve my diagram
Use case:
In order to submit a link on this application users have to provide all the required ...
2
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1answer
13 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 ...
1
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0answers
10 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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0answers
24 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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42 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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1answer
28 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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1answer
20 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
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1answer
17 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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0answers
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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0answers
19 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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12 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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0answers
42 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 ...
1
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1answer
36 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 ...
2
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0answers
23 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 ...
0
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1answer
36 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 ...
1
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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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0answers
41 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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0answers
26 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?
0
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1answer
57 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 ...
1
vote
1answer
38 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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0answers
26 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 ...
0
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1answer
93 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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25 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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28 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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0answers
11 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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0answers
38 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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0answers
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.
0
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1answer
19 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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0answers
35 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
105 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
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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2answers
85 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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0answers
34 views
In index allocation scheme, what parameters does the maximum size of a file depends on?
My understanding is as follows:
...
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0answers
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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0answers
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 ...
0
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1answer
44 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: ...
0
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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 ...
2
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1answer
219 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 ...
0
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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 ...
1
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1answer
50 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 $(1, 4, 15)$, ...
1
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1answer
192 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. ...
1
vote
2answers
346 views
how to get rows with more than 1 appearance of a specific column in relational algebra
I have a table like this:
...
0
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0answers
12 views
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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0answers
24 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 ...
0
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1answer
31 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....
0
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1answer
28 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?
0
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1answer
73 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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0answers
23 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→...
