When Is Denormalization Good? {3}

by Hieu H
Database normalization is a process in which redundant and duplicate data is reduced. Normalization provides a more readable and organized database. In fact, it is what most database professionals are taught to do and is normally considered a good practice. Denormalization is the exact opposite. In the denormalization process, you take a normalized database of different tables and “combine” them, essential going backwards in the normalization forms. There are certain instances in which this may be beneficial. The pro of denormalization is that access to records are generally faster. SELECT queries perform better and are less complicated because there are less JOIN statements. The cons of denormalization are that INSERT and UPDATE queries take longer. In instances where there are drastically more SELECT queries than INSERT or UPDATE queries, denormalization makes sense and the performance increases greatly outweigh the cons. read more...

Synchronizing database on mobile devices {2}

by Ricardo C
This article relates to the synchronization between mobile devices and databases. Since mobile technology as advanced and equipment have led to the emergence of a new computing environment and a variety of small sized mobile devices such as smartphones and PDAs that has been popularized. The problem is that mobile devices do not have much computing power and they rely on batteries; constant access to network is difficult due to narrow bandwidth. Mobile devices need to download the database when connected and then work off-line and by doing so there are inevitable inconsistencies between the server-side database and the mobile database. Commercial DBMS vendors offer solutions to maintain the database synchronized between the two devices however these solutions are dependent of the server-side database using dependent information such as metadata. Because of these restrictions, the extensibility, adaptability and flexibility of mobile business systems are markedly decreased. The article suggests the implementation of SAMD (Synchronization algorithms based on message digest) which resolves synchronization problems using only standard SQL queries. The SAMD makes the images at the table of the server-side database and the mobile database using a message digest algorithm; then the images and the message digest values are saved in the message digest tables on both sides. The images are compared and select the rows needed for synchronization. The SAMD would provide extensibility, adaptability and flexibility. read more...