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

learn more… | top users | synonyms

2
votes
1answer
27 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 ...
0
votes
1answer
19 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 ...
-1
votes
0answers
16 views

Serialization graph - confusion

I don't know how to produce a serialization graph from the following information. As where I've highlighted every possible Read/Write, Write/Read and Write/Write. They are dealing with different ...
0
votes
1answer
16 views

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

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: ...
0
votes
0answers
16 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 $m$ ...
0
votes
0answers
53 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 ...
1
vote
0answers
35 views

Concurrency Control: Two phase locking

A schedule is given as follows: TI:R(X) T3:R(Y) T2:W(X) T3:W(Y) T3:R(X) T1:R(Y) T2:W(Y) where R(X)=read x and W(X)=write x Is this schedule executable under two-phase locking protocol with upgrade ...
0
votes
1answer
23 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 ...
2
votes
0answers
41 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
votes
0answers
60 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?
0
votes
1answer
48 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 ...
0
votes
1answer
25 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?
-1
votes
1answer
75 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 ...
0
votes
0answers
13 views

is it possible to combine 2 relation with an entity set for rdbms minimization?

E1 is a weak entity set. E2 and E3 are other two entity sets. E1 is related to E3 via a weak relation R1 cardinality is many to 1 and E1 is connected to E3 via R2 with cardinality many to 1. Now in ...
1
vote
2answers
70 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) ...
0
votes
1answer
33 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 ...
2
votes
0answers
75 views

What is a best known algorithm for finding diameter of undirected graph?

What is best known algorithm (approximate or exact) for finding diameter of a large undirected graph? The diameter is defined as longest of shortest paths between any two nodes. I know that naive ...
3
votes
1answer
78 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 ...
0
votes
2answers
58 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
votes
1answer
174 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 ...
5
votes
1answer
70 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 ...
1
vote
0answers
21 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 $1$-$\text{SR}$. ...
0
votes
0answers
20 views

Isomorphism of the cores of two symbol universes implies equivalence

We know that an isomorphism exists between two symbol universe of CQ expressions $\psi$ and $\phi$, $A_\psi$ and $A_\phi$ and $symb(\psi) = symb(\phi)$ iff $\psi \equiv \phi$. But given only that ...
0
votes
1answer
167 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) ...
1
vote
1answer
45 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 ...
0
votes
1answer
43 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: ...
-2
votes
1answer
49 views

How 3NF and BCNF are different in terms of candidate key?

The original definition of third normal form (3NF) was inadequate in some situations. It was not satisfactory for the tables: - that had multiple candidate keys - where multiple candidate keys were ...
0
votes
0answers
30 views

Difference between parallel and concurrent buffering?

In double buffering there are two terms Concurrent buffering. Parallel buffering. What is the difference between them, answer with example will be appreciated.
1
vote
0answers
46 views

Does 4NF imply BCNF?

Wiki says: 4NF is the next level of normalization after Boyce–Codd normal form, but I can not see how the definition of 4NF implies BCNF. Consider the relation with 3 attributes: Country, ...
1
vote
1answer
48 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 ...
0
votes
1answer
198 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 ...
0
votes
0answers
87 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 ...
0
votes
0answers
31 views

Definition of 3NF

We've been studying relational database design in the last semester, and I was missing a lot of lecturers, so I decided to stick to the course's book, Database Systems; The Complete Book, to make up ...
2
votes
1answer
59 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 ...
0
votes
1answer
85 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
votes
1answer
31 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 ...
0
votes
0answers
29 views

1NF to 2NF, do the functional dependencies remain?

When decomposing from 1NF to 2NF, is there a guarantee that the functional dependencies don't change in regards to the original relation? Example: ...
1
vote
1answer
33 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: ...
0
votes
1answer
83 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 ...
0
votes
1answer
156 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?
1
vote
1answer
99 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 ...
2
votes
2answers
162 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 ...
1
vote
0answers
27 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 ...
0
votes
1answer
303 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?
1
vote
0answers
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 ...
1
vote
2answers
90 views

Functional Dependencies and BCNF

Consider the following schema: Students(Id, Name, AdvisorId, AdvisorName, FavouriteAdvisorId) What are the functional dependencies here? Ir seems that it would ...
1
vote
1answer
359 views

Why is the Mean Time To Failure of multiple disks calculated via division and not multiplication?

I am reading about disk redudancy. I read the following: Suppose that the mean time to failure of a disk is 100,000 hours. Then the mean time to failure of some disk in an array of 100 disks ...
2
votes
0answers
61 views

What happened to Active Databases?

When reading the literature on declarative programming technology. A particular technology that sounded promising is active databases. It essentially allows the programmer to specify rules about data ...
1
vote
0answers
41 views

In database query theory, why do we not want to use a constant that isn't in the dictionary?

A badly explained textbook example asks the following: Suppose we have a definition of the dictionary our database will use (that is, it's relations and constants), defined as: $<R_\le (?, ?), ...
2
votes
3answers
272 views

What is the difference between Transitive Closure and Join?

In database theory, there is a notion of transitive closure over relations. I am wondering if join operator over relations is also a special case of transitive closure?