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17
votes
5answers
3k views

Why must uncommitted transactions be undone in backwards order?

I have a database log where some transactions win (they are committed before crash) and some lose (not committed yet). We learned in class that the losers' actions have to be undone backwards. Is ...
3
votes
1answer
47 views

blockchain database - why so redundant

I've become interested in blockchain databases. Everywhere I've read it said that each user has to have his/her own copy of database. Why can't distributed blockchain database be 'distributed' to ...
0
votes
0answers
34 views

Idempotence when replaying committed transactions

I'm trying to understand recovery mechanisms in transaction management. When a failure occurs then committed transactions are redone. Why is this required? How is this done repeatedly without ...
0
votes
0answers
26 views

Proof of RAP-derivation sequence for a set of functional dependencies in relational databases

I'm reading David Maier's outstanding but out-of-print book on relational databases (the book,"The Theory of Relational Databases", is available online from the author's website http://web.cecs.pdx....
0
votes
0answers
27 views

Linear hashing vs extendable hashing - memory

could you give me an example when linear hashing costs more memory than extendable hashing? And the other side, when extendable hashing takes more memory than linear hashing?
0
votes
0answers
10 views

Entity relationship with two relationships between entities

I came across this slide and was very confused. This is the case of two relationships between the entities which are the opposite direction. This ERP for me seems to mean that all Staff manage ...
3
votes
1answer
39 views

Is there a fundamental CS problem in ORMs that leads to N+1?

Many of us are familiar with N+1 problem when working with database queries. The problem was known before ORMs (Object-relational mapping frameworks) came around, but it seems that ORMs exacerbated it....
0
votes
0answers
10 views

Grouping operator in DBMS (Ɣ) is duplicate impervious. Why?

I'm reading Database Systems by Ullman where its mentioned that Ɣ is duplicate impervious. I dont understand why a simple group operation should cause elimination of duplicates. Aliter, Duplicate-...
2
votes
2answers
33 views

Restricting capabilities of admin role in database schema

Suppose I have to design database for learning management system. Which will going to have user having roles such as admin, teacher, tutor, student etc. In a system student can submit solution for an ...
4
votes
1answer
243 views

What is the difference between a R-tree and a BVH?

I've just read about R-Trees: The key idea of the data structure is to group nearby objects and represent them with their minimum bounding rectangle in the next higher level of the tree; the "R" ...
0
votes
1answer
28 views

Lookup complexity in B-trees [Database]

Given that: B = n/R blocks in the file 2d index records per block (blocking factor): 2d > R an extra block access from the index to the datafile I am not able ...
1
vote
1answer
417 views

Need help with ER diagram

I am making database on Disaster Management. There are four tables. ...
0
votes
0answers
42 views

What is the difference between physical level and internal level of a database according to ANSI/SPARC?

According to ANSI/SPARC model a database consists of three (or four?) levels. These are internal (and/or physical?), conceptual and external levels. Most information resources say like physical and ...
0
votes
2answers
78 views

What is the difference between F+ (closure of F) and F* (cover of F) for Functional Dependencies?

F+ and F* is defined as follows: F+: closure of F F+ = {fd | F |= fd} Set of all FDs deduced from inference rule (normally: Armstrong axioms) F: cover of F {fd | F |- fd} cover of F Set of ...
0
votes
1answer
60 views

An ID (auto increment integer) always as primary key for each db-table? [closed]

Till now, I always gave each db-table an id-column (generally with the table name and an underscore as a prefix, e.g. employee_id), and I also never have seen another approach to unique a db-table-...
0
votes
1answer
79 views

Why isn't there a universal separator character for data files? [closed]

I am not sure if this is the correct forum for this question, but... After so much time and usage of spreadsheets and data files in general, there is a need to cater for all types of files containing ...
0
votes
0answers
28 views

Pointers to schema evolution and semi-automated instance migration

QUESTION EDITED Since this question wasn't clear, I'll rephrase. See question-history for original. I'm looking for academic papers that describe schema evolution on documents (1) in a generic way. ...
0
votes
1answer
29 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?
0
votes
0answers
15 views

Question about 3NF Form

So I was given set of productions and have ocmputed minimal cover. However, I have to change the set to 3NF form. I know that a production(X->A) is in 3NF form if one of these statements is true: 1)...
0
votes
0answers
40 views

2 phase locking with added increment mode

Suppose that a DBMS recognizes increment as an atomic operation, in addition to the read and ...
3
votes
2answers
69 views

The finer details of Meek's STV

Meek's version of the Single Transferable Vote system [.pdf] is used in multiple big elections including those of New Zealand and Stack Exchange. Demonstration (with thanks to the Department of ...
1
vote
0answers
955 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 ...
2
votes
0answers
38 views

Using cross-products with relational algebra

I have some questions about something that I'm working on in an assignment for my database class. Here is the schema for the questions I'm working on, so that you know what to refer to: ...
0
votes
1answer
100 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), w3(Z)...
-3
votes
2answers
41 views

An application where we always delete the oldest object? [closed]

In what king of application, in which we insert or delete objects, we always delete the oldest one (the least recently stored, more precisely which was the first object stored) ?
10
votes
2answers
184 views

Good snapshottable data structure for an in-memory index

I'm designing an in-memory object database for a very specific use case. It is single writer, but must support efficient concurrent reads. Reads must be isolated. There is no query language, the ...
1
vote
1answer
86 views

Data versioning in a relational database

I've been working on an industrial project where my job was to design a data model in-memory and in a relational database in such a way, that can capture the time-varying nature of the production ...
5
votes
1answer
281 views

How to find a basis which is guaranteed to need 9 or less characters to represent a 12 digits number?

I'm trying to map a 12 digit number into a fixed width file. For a number of reasons, it must be compressed in such a way that it is guaranteed to be less than or equal to 9 characters (alpha numeric ...
3
votes
1answer
73 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 ...
5
votes
1answer
414 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 ...
2
votes
0answers
27 views

How to store linguistic data?

I'm both interested in practical and theoretical aspects of the problem. How do you store linguistic data. Suppose you have stemmed, parsed, tagged and, perhaps even did some preliminary analysis, ...
0
votes
1answer
70 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 ...
0
votes
1answer
2k 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: ...
1
vote
0answers
74 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 ...
0
votes
1answer
50 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 ...
3
votes
2answers
251 views

Linearizability and Serializability in context of Software Transactional Memory

I've been trying to grasp serializability and linearizability in the context of software transactional memory. However, I think both notions can be applied to transactional memory in general. At this ...
3
votes
0answers
138 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 following,...
0
votes
1answer
99 views

Information Systems (IS) and Data Warehouse

I'm working on a research project about the adoption of DWH systems and doing some literature review I find many documents that refer to Information System. I tried to find the right definition of ...
2
votes
1answer
149 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?
4
votes
1answer
99 views

n closest points in a set of lat/long coordinates

Here's my problem: I have a website where people can search based on their location (which is converted to lat/long coordinates). I have many products stored in a database with their lat/long ...
-1
votes
0answers
56 views

Could there be an end of (human-organized) databases? [closed]

I'm not a computer science guy but just curious about a potential decline of databases. I believe there will always be data, that's for sure, but would there always be databases? Databases are a ...
0
votes
1answer
38 views

Terminology for describing a kind of server [closed]

What is the adjective used to describe the fact that a server keep track of queries made by a user. I take the example of a database server.
2
votes
2answers
328 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) ...
3
votes
1answer
394 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 ...
1
vote
0answers
45 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 $1$-$\text{SR}$. ...
1
vote
1answer
120 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 ...
2
votes
1answer
120 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
199 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: ...
1
vote
2answers
734 views

B-Tree and how it is used in practice

I understand what a B-Tree is (I already implemented a B-Tree in Java with insert and delete methods that preserve the invariant). However I do not understand exactly how it is used for example for ...
3
votes
1answer
7k views

Difference between data duplication and data redundancy

My Computing teachers talk about data duplication and data redundancy in terms of databases as different things, but I'm struggling to differentiate them. The context is database normalisation, and in ...