Course: Database Systems Discussion 1 (Chapter 23): What are the main reasons for an potential advantages of distributed databases? Instructions: Your response to the initial question should be 350
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Post 1:
2 days ago
Ramya
Discussion
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What are the main characteristics of NOSQL systems in the area related to data models and query languages.
NQSQL Database is a non-relational Data Management System, that does not require a fixed schema. It avoids joins, and is easy to scale. The major purpose of using a NoSQL database is for distributed data stores with humongous data storage needs. NoSQL is used for Big data and real-time web apps. For example, companies like Twitter, Facebook and Google collect terabytes of user data every single day. NQSQL database stands for Not Only SQL or Not SQL. Though a better term would be NoREL, NoSQL caught on. Carl Strozz introduced the NoSQL concept in 1998. Traditional RDBMS uses SQL syntax to store and retrieve data for further insights. Instead, a NoSQL database system encompasses a wide range of database technologies that can store structured, semi-structured, unstructured and polymorphic data. The concept of NoSQL databases became popular with Internet giants like Google, Facebook, Amazon, etc. who deal with huge volumes of data. The system response time becomes slow when you use RDBMS for massive volumes of data. To resolve this problem, we could scale up our systems by upgrading our existing hardware. This process is expensive. The alternative for this issue is to distribute database load on multiple hosts whenever the load increases. This method is known as scaling out. NoSQL databases never follow the relational model. Never provide tables with flat fixed-column records. Work with self-contained aggregates or BLOBs. Doesn't require object-relational mapping and data normalization. No complex features like query languages, query planners,referential integrity joins, ACID. NoSQL databases are either schema-free or have relaxed schemas. Do not require any sort of definition of the schema of the data. Offers heterogeneous structures of data in the same domain.
Reference:
Wiese, Lena. Advanced Data Management : For SQL, NoSQL, Cloud and Distributed Databases . Berlin ;: De Gruyter,, 2015. Web.
Editorial Team. (2014, May 25). What Is a Distributed Database, and What Are Distributed Data Systems For?Atlantic.Net. https://www.atlantic.net/vps-hosting/about-distributed-databases-and-distributed-data-systems/
Altarade, M. (2016, December 15). The Definitive Guide to NoSQL Databases. Toptal Engineering Blog. https://www.toptal.com/database/the-definitive-guide-to-nosql-databases
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Post 2:
3 days ago
Sai Deepthi
week 6
COLLAPSE
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In designing a database, for the purpose of minimizing redundancy, we need to collect a set F of functional dependencies (FD) that reflect the constraints of the underlying application. Ideally, we do not want to miss any FD, i.e., we want to obtain an F that is as large as possible. However, in practice, FD collection is a difficult process. No one can guarantee always discovering all FDs. A Closure is a set of FDs is a set of all possible FDs that can be derived from a given set of FDs. It is also referred as a Complete set of FDs. If F is used to donate the set of FDs for relation R, then a closure of a set of FDs implied by F is denoted by F+. Let's consider the set F of functional dependencies given below:
F = {A -> B, B -> C, C -> D}
from F, it is possible to derive following dependencies.
A -> A ...By using Rule-4, Self-Determination.
A -> B ...Already given in F.
A -> C ...By using rule-3, Transitivity.
A -> D ...By using rule-3, Transitivity.
Now, by applyiing Rule-6 Union, it is possible to derive A+ -> ABCD and it can be denoted using A -> ABCD. All such type of FDs derived from each FD of F form a closure of F. Steps to determine F+example:
Determine each set of attributes X that appears as a left hand side of some FD in F.
Determine the set X+ of all attributes that are dependent on X, as given in above example.
In other words, X+ represents a set of attributes that are functionally determined by X based on F. And, X+ is called the Closure of X under F.
All such sets of X+, in combine, Form a closure of F.
References:
Putra, Eko. 2013. "What is the Definition of Databases? Functions and Components in the Data Base Management System (DBMS) ". http://ilmudatabase.blogspot.com/2013/11/PengertianDatabase-itu-What-Function-and-Komponen-pada-Data-BaseManagement-System-DBMS.html, accessed 20 March 2014.
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