the analytic study of ways in which information is efficiently and effectively stored to and retrieved from computer systems.

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Does the following modified Two-Phase Locking protocol ensure serializability and freedom from deadlock?

Consider the following variant of the two phase locking protocol. Suppose a transaction $T$ accesses (for read or write operations), a certain set of objects ${O_1,...,O_k}$. The modified algorithm ...
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2answers
35 views

Relational query for universally quantified formula

My university is participating in the implementation of a library borrowing managing system at Richelieu National Library in France. I received the order to formulate the query: "find all users ...
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43 views

Describe data structure using equations

Good afternoon. At work I'm currently developing a system which takes user input (well structured) and then stores it in memory to do some processing. The input is basically a dataset formed by ...
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1answer
28 views

Does the conservative two phase locking protocol produce cascadeless schedules?

Let us consider the following schedule : \begin{array}{lcr} \mbox{$T_1$} & \mbox{$T_2$}\\ \\ \mbox{lock-exclusive(a)} \\ \mbox{lock-exclusive(b)} \\ \mbox{read(a)} \\ \mbox{a=a+50} \\ ...
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21 views

How can I solve this Functional Dependency?

Consider R(A, B, C) with FDs F ={A→B, B→C, A→C} Prove or disprove F |= C → A There are 7 inference rules from Armstrong's Axiom. Which one is to use here?
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61 views

State of the art time complexity for getting (tree) descendants by type/attribute

Let's say I have a tree comprised of nodes where each node is of some type (T), where there is a known/fixed number of types (i.e. similar to attributes in an xml document), and where a node can only ...
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655 views

Difference between conflict serializability and view serializability

In my understanding both of them can be converted to serial schedules. (This helps with consistency by isolation property while also giving the performance boost by concurrency). I'm unable to ...
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59 views

how to compute functional dependencies and MVDs after decomposition?

Let's say we have a relation $R$ with a set of functional and multivalued dependencies $F$, and we found a dependency that violates some normal form. Then we decompose $R$ into $R_1$ and $R_2$. How to ...
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1answer
80 views

A schedule is not conflict-serializable. Is it serializable?

While reading this solved quiz on concurrency control, I got stuck on exercise 2, which reads as follows: 2) Consider the following schedule: S: r1(X), w2(X), r3(X), r1(Y), w2(Z), r3(Y), ...
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33 views

Conjunctive Regular Path Queries and Subgraph Isomorphism

How do conjunctive regular path queries and subgraph isomorphism relate to each other? It seems that conjunctive regular path queries are a specialised form of subgraph isomorphism. The follow is ...
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61 views

Adaptive Radix Tree - Question regarding child indexing

i have to write an exam in a course given by one of the contributing professors of this paper: http://www-db.in.tum.de/~leis/papers/ART.pdf Of course this could also be a possible topic in the exam. ...
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19 views
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61 views

Algorithm for automatic/optimal database joins?

I'm curious if there is existing literature or well known algorithms out there for a problem I am working on. Given a normalized relational database with valid foreign key constraints and a list of ...
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1answer
362 views

A relational algebra extended to model the full DML (“CRUD”) domain

There are multiple references about the relational algebra for modeling queries (SELECT) but I have found very very little on the expanded algebra that would ...
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1answer
41 views

Does XML covers the representation of any structured data and knowledge

I see nowadays XML is used to structure any file or data. It can represent the flat and hierarchical relations. It even can be used to show the parse tree of a sentence in a natural language. I am ...
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1answer
1k views

What is the difference between “strict schedule” and “cascadeless schedule”?

In database transactions theory, what is the difference between a strict schedule and a schedule that is merely secured against cascade aborts? Could you give an example of a schedule that is ...
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61 views

Database normalization impractical

After third form normalization, extra tables shall be created. And the functional determinant are used as primary key in the new table, as foreign key in the modified old table. My question is that ...
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1answer
916 views

What is the difference between a prime attribute and a proper subset of the candidate key? [closed]

I am taking DBMS classes and am currently studying the various normal forms. The following is the definition of a Prime Attribute I learned in class: ...
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0answers
41 views

Algorithm to test dependency preservation

Is there an algorithm to test whether the decomposition of relation $R$ into relations $R_1,\dots,R_n$ is dependency-preserving? In more detail, I am given a relation $R(x_1,\dots,x_m)$ on $m$ ...
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68 views

two phase locking and a contest question?

In 2PL (two phase locking), what advantage(s) does the rigorous model have over the strict model? I) There is no advantage over the strict model. II) In contrast to the strict model, it ...
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1answer
38 views

How can I formalize key value stores with set theory?

I'm currently developing a simple key-value NoSQL store and want to build its formal model. I found article about key value formalisation with category theory, but I'm interested are there some works ...
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97 views

How to generate globally unique timestamps for transactions in distributed database systems?

According the paper [1] (Section 4), timestamp ordering (T/O) is a technique whereby a serialization order is selected a priori and transaction execution is forced to obey this order. In the ...
2
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0answers
102 views

Rollback and Timestamp Ordering in Database

If we use the Timestamp Ordering for concurrency control in following scheduling: My TA says T2,T3,T5 is Run and T4,T5 is Rollback. I think it's false. any expert could help us?
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1answer
721 views

Finding the Candidate Keys of a Relation Using the FD's

I have definitely checked out many different related posts. I have also done different sample problems from online sources as well from a similar problem. However, I am stuck on the problem below ...
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1answer
30 views

Can there be a strict transaction that is not 2Phase?

I am confused about the definition of a strict transaction. What is the difference between a transaction that is strict and a transaction that is both strict and 2 phase?
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1answer
142 views

Naive Bayes MapReduce

I have the following question to answer in a MapReduce assignment sheet The Naive Bayes classifier is a widely-used tool for analyzing data. Consider a data set that has $n$ data items, each of ...
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2answers
234 views

When should you use the existential and universal quantifiers for Relational Calculus?

Could someone explain to me WHEN do you use existential and universal quantifiers for Relational Calculus? Given this schema: Hotel(hotelNo, hotelName, city) ...
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1answer
765 views

What is the difference between Strict 2Phase Locking and 2Phase Locking?

I have read some notes about the two but yet still confused about why there is a need for the strict 2phase locking. Based on some slides, Two Phase Locking and Strict Two Phase Locking They have ...
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1answer
188 views

Partial order, total order, and version order in transaction histories

In Section 3.1.2 "Transaction Histories" of the PhD thesis by Atul Adya [1]: A history $H$ over a set of transactions consists of two parts: (1) a partial order of events $E$ that reflects the ...
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2answers
61 views

Understanding transactions

In operating systems, Is a transaction a process? Are they the same concept? Does a transaction have the same meaning in database management systems, as in OS? A database book says A ...
3
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1answer
336 views

Can a schedule with cyclic precedence graph still be serialisable?

We know Every conflict serializable schedule is serializable, but not all serializable schedules conflict-serializable. (*) so it means there is at least one serializable schedule that not conflict ...
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1answer
115 views

Why do relational databases use 2PC for distributed transactions over the likes of Paxos?

Paxos is more powerful and in the famous writing "Consensus on Transaction Commit" : http://research.microsoft.com/pubs/64636/tr-2003-96.pdf, Jim Gray and Leslie Lamport describe 2PC as a special case ...
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32 views

1-serializability theorem in database theory

In the paper "MVCC@TODS'1983 by Bernstein et al.", 1-serializability ($1$-$\text{SR}$) problem is defined as a decision problem: To decide whether an MV (multi-version) log $L$ is $1$-$\text{SR}$. ...
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1answer
350 views

BCNF Decomposition: Confusion regarding given answer

I encountered the following question: Given a relation R(A, B, C, D) with the following functional dependencies: A -> B, C -> D, B -> C. The BCNF Decomposition of R is: A) {(A,B), (C,D), (B,C)} B) ...
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1answer
69 views

Applying Brewer's theorem (CAP) to a single node

I'm going through Brewer's theorem and its proof by Nancy Lynch and Seth Gilbert. But the paper left me with one question. What prevents the theorem from being applicable to a single node? I haven’t ...
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1answer
51 views

Composition for Functional Depedencies

Suppose I have the following Functional Dependencies for a Relational Model: $A \to C$ $B \to C$ According to the composition rule for functional dependencies we have: ...
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1answer
89 views

A relationship in a UML class diagram

I am investigating a small database in a paper: Each line is a selling record. For instance, Line 2 expresses that ...
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2answers
2k views

Use count() in relational algebra

Person(name, phone) Mike 456-789 Mike 123-456 John 230-785 $\dots \dots$ How to get those people who have more than one phone numbers with relational algebra? This sounds simple, but I am ...
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191 views

convert domain relational calculus with two same tuples to relational algebra

Given two relations $R(A, B)$ and $S(A, C)$. I can understand the early part is the projection of attribute $A$ from $S$, which could be written as $π_a(S)$, but later part is confusing and not ...
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1answer
77 views

What actually is the concept of transparency? Why not call it Abstraction?

I searched this over Google few times but ended up with articles on transparency rather than an answer. With relation to distributed database study(or distributed OS), what is the concept of ...
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1answer
154 views

Automatically generate meaningful queries for a data table

My field of research is not Database or AI. But I have some problems to solve, and would like to know which branch this kind of problems belong to, and what are the results. The main question is: ...
2
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1answer
41 views

Can A still be a key if two tuples are the same

I am studying database functional dependency. It says if A can functionally determine all other attributes, it is considered to be a key. What if 2 tuples are exactly the same, can we still say A is ...
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1answer
38 views

Functional Dependencies in Relations

I'm currently reading about functional dependencies. I've read Armstrong's axioms about: Relexivity: $if$ $B\subseteq A$ $then$ $A\to B$ Augmentation: $if A\to B$ $then$ $AC\to BC$ Transitivity: ...
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1answer
90 views

Functional dependencies with the same key?

let's consider a table with carID | hireDate | manufactory | model | custID | custName | outletNo | outletLoc I want to evaluate all the functional dependencies ...
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1answer
355 views

Boyce-Codd Normal Form vs. 3rd Normal Form

Any schema that satisfies BCNF also satisfies 3NF. But how can this be true if BCNF does not necessarily guarantee dependency preservation, whereas 3NF guarantees dependency preservation?
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1answer
153 views

What is the intuition that 2-phase locking achieves serializability (also known as before-or-after atomicity)?

I am learning 2-phase locking and its unclear to me how it achieves/guarantees before-or-after atomicity (i.e. serilizability). I went to the following notes ...
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2answers
253 views

Can you reduce a precedence graph or do *all* relevant nodes need to be connected

Let's say we have the following simple transaction-schedule: T1 | T2 | T3 -----+------+----- w(x)| | | w(x) | | | w(x) T1 comes before ...
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0answers
28 views

How to display distinct rows from single column without using DISTINCT keyword and count() function? [closed]

How to display distinct rows from single column without using DISTINCT keyword and [having count(*) > 1 ] ? My question is can we do this using sub-queries or co-related sub query ? If yes how we can ...
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1answer
580 views

Clustered index is dense or sparse?

I am confused about clustered index is dense or sparse. I searched for that, sources saying it is sparse, but can be dense also. What is it exactly?
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13 views

Multvalued Dependencies [closed]

Suppose we have the following schema: Drinkers(name, addr, phone, beersLiked) Also suppose $\text{name} \twoheadrightarrow \text{phone}$. Consider the following ...