Technology Questions

Data warehousing is a process of repository of electronic data of an organization. For the purpose of reporting and analysis, data warehousing is used. The essence concept of data warehousing is to provide data flow of architectural model from operational system to decision support environments. 

There are many algorithms that can be used to analyze the database to check the maintenance of all the data sets that are already present. The different types of cluster models include as follows:

- Connectivity models: these are the models that connect one cluster to another cluster. This includes the example of hierarchical clustering that is based on the distance connectivity of one model to another model. 

- Centroid models: these are the models that are used to find the clusters using the single mean vector. It includes the example of k-means algorithm.

- Distribution models: it includes the specification of the models that are statistically distributed for example multivariate normal distribution model.

- Density models: deals with the clusters that are densely connected with one another in the regions having the data space. 

- Group models: specifies the model that doesn’t provide the refined model for the output and just gives the grouping information

Advantages of 3G:

- Overcrowding is relieved in existing systems with radio spectrum
- Bandwidth, security and reliability are more
- Provides interoperability among service providers
- Availability of fixed and variable rates
- Support to devices with backward compatibility with existing networks
- Always online devices – 3G uses IP connectivity which is packet based
- Rich multi media services are available

Disadvantages of 3G:

- The cost of cellular infrastructure , upgrading base stations is very high
- Needs different handsets.
- Roaming and data/voice work together has not yet been implemented
- Power consumption is high
- Requires closer base stations and are expensive
- Spectrum-license costs, network deployment costs and handset subsidies subscribers are tremendous.

SELECT * FROM table_name ORDER BY column_name desc Fetch first 5 rows only;

Node.js uses a single threaded model with event looping.

A cookie is a small text file on the client machine either in the client’s file system or memory of client browser session.

Both these are used to combine the results of different SELECT statements.

    UNION       - Selects only distinct values 

    UNION ALL - Selects duplicate values also

Syntax:

    SELECT column_name(s) FROM table1

    UNION / UNION ALL

    SELECT column_name(s) FROM table2;

Notice that each SELECT statement within the UNION must have the same number of columns. The columns must also have similar data types. Also, the columns in each SELECT statement must be in the same order.

CURSOR STABILITY:

- CS is a row level locking

- Acquires an exclusive lock on the row that is to be updated

- When the control is moved to the next updatable row, the lock is released

REPEATABLE READ:

- RR is a page level locking

- Acquires an exclusive lock on the entire page which is the source of row availability

- When the control is moved to the next updatable page the lock is released