# Questions tagged [db.databases]

Theoretical questions in Databases

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### What are the most known database disk storage layout algorithms?

I can list for example algorithms used in databases: append only b-trees (MVCC like used in CouchDB) merged logs (like used in Big Table, Hbase, Cassandra) paged storages grouped in extents (like in ...
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### How to understand the "Availability" of the CAP theorem?

As we know, in the CAP theorem, "A" means "Availability". On wikipedia, the explanation of "Availability" is: Availability: a guarantee that every request receives a response about whether it was ...
976 views

### What is DDL (Data Definition Language)?

As a part of my curriculum, I am studying principles of DBMS from the book by Silberschatz and Korth. A part of it is about Data Definition Language (DDL). I ...
218 views

### What are good set size estimation algorithms for small sets (around 10-50 elements)?

I'm trying to implement an online distinct counting algorithm, and I have thousands of small sets of 32 bit IP addresses whose sizes I want to estimate with high accuracy (1-5%). I came across quite ...
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### Minimize a datalog program

We can consider a datalog program as a set of clauses. Some of them allow to derive others. For instance from: A(x) :- B(x), C(x). B(x) :- D(x). C(x) :- D(x). We ...
283 views

### Find all items which are subsets of an item

I have a problem that I think should have been studied. I am looking for algorithms for it. Each item is a set of key-value pairs. Let $x$ be an item and $F$ be a set of items. Each key and each ...
709 views

### Relational Algebra - Natural Join [closed]

So I got two relations with two common attributes. For one of those attributes, the attribute values in two of the tuples of those relations are the same, for the other they aren't. How does my result ...
386 views

### logic in the presence of doubt, uncertainty, lies

I was reading Harry Frankfurt's On Bulls*t, a 1986 philosophical essay about this blurry notion between truth and falsity. This is not a gratuitous exercise. This may have applications to computer ...
513 views

### How do you argue a query is impossible in a query language like SPARQL or SQL?

I've been investigating the ability of the SPARQL query language to represent certain basic tasks in graph theory and machine learning, and have come to believe that it is not possible to do some. For ...
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### How to go about proving the basic operators in relational algebra are independent of each other?

The five basic operator select, project, cross, union and diff in relational algebra are independent of each other. I'm trying to formally prove this statement but can only progress for cross product ...
154 views

### Combining multiple time-based datasources with different periods

I have two time-based data sources (one providing data by month and the other by week) that must be combined to create a third daily source (recognizing that at best we're getting one possible ...
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### Can we do joins in NC?

Suppose we want to join two relations on a predicate. Is this in NC? I realize that a proof of it not being in NC would amount to a proof that $P\not=NC$, so I'd accept evidence of it being an open ...
224 views

### Relational model for data structure reasoning

I am trying to find out if there is any work on applying the Codd's relational model (underlying relational databases) for reasoning about linked data structures. Any connections with UML models and ...
617 views

### Is analogy between database and probability concepts legitimate?

In Relational Databases: Tutorial for Statisticians Joe R. Hill casts probability view onto database theory. In Table 1 the author summarized the parallels between the two disciplines, describing ...
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### Lower bounds on batched query search

I am not much in the field of databases. But the problem I m facing is the following: given a database $D$, we receive a batch of distinct queries $Q = \{q_1, ..., q _k\}$, where each $q_i$ is a ...
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### How to automatically generate indexes and preaggregations from queries

This question might be a little ill-specified, but the idea I want to explore is: User writes a bunch of queries that they want to perform over some data (for concreteness, just consider it a read-...
795 views

### What are recent advances in relational databases?

I'm wondering what are recent advances in relational database theory and related domains? I'm interested in new approaches, query languages (alternatives to SQL and/or extensions to it), products (...
341 views

### Transactional partially-ordered message queuing

I'm having a really hard time finding a solution to a practical programming problem, and I think raw CS might have an answer. The requirement is for a familiar message queue for which there are ...
861 views

### Canonical forms for relational algebra expressions

I'm looking for whatever work may exist, or thoughts people have, on the question of whether/to what extent there exist(s) one or more canonical form(s) to which relational algebra expressions may be ...
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### Purely Functional Equivalent of B-Tree?

I am exploring the idea of writing a DBMS in purely functional way. The traditional data structure used for indexing is B-Tree. I'd like to know some purely functional equivalent of B-Tree that would ...
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### DATALOG references

What are the best references for self study in DATALOG? I am particularly interested in expressive power, complexity results, evaluation methods, extensions of DATALOG with negation etc. Are there any ...
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For those doesn't know about linear datalog, linear datalog is a datalog rule in which the number of IDB predicate in each rule is less or equal than one. My question is, why is this interesting? ...
419 views

### Database query languages for efficient queries

It seems that in popular query languages for relational databases, it is possible to create queries that will require a lot of resources to answer. In practice, database admins manage this by limiting ...
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### Producing more functional dependencies (FDs) from a list of functional dependencies (FDs) [duplicate]

Possible Duplicate: Producing more functional dependencies (FDs) from a list of functional dependencies (FDs) I am currently trying to understand functional dependencies and their properties. I ...
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### Data structure that allow efficient tag based lookups

I am looking for a highly efficient data structure for storage of data similar to the following. Id Tags Order1 Order2 -------------------------- 1 1,2 1 1 2 2,5 2 3 3 ...
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### Getting started with Hashing for Information retrieval

I recently finished my bachelors and now work on Cross-lingual language search. I want to get started in hashing and see how they are useful in information retrieval. (Yes, I know what hashing is), ...