A Boston Technical Recruiters Blog

A dead lock. This occurs when two transactions wait for each other to unlock data.

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A lock gives a transaction exclusive use of a data item for the duration of the transaction. This is important so you do not run into concurrency control issues where two or more users are trying to perform queries on the same set of data. There are several levels of locks known as lock granularity starting with the database-level lock that prevents access to the entire database, this is followed by the table level lock that locks an entire table, a page level lock locks a disk page and is the most frequently used DBMS locking device. A row level lock locks the row, while the field level lock allows transactions to access the same row.

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Concurrence control ensures Serializabilty in a  multiple user database. The first common problem is lost updates which occurs when data an operation from T2 uses un committed date from the same table of transaction T1. The uncommitted date problem arises when two transactions T1 and T2 are executed concurrently but the T1 is rolled back after T2 used data from T1. Inconsistent retrievals occur when a transaction calculates aggregate functions while a second transaction updates those functions in real time.

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Atomicity, Consistency, Isolation, Durability, and Serializability(ACIDS).

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E-commerce is a relatively new invention as far as commerce is concerned and therefore has not completely stabilized. There is a vast amount that people do not know about e-commerce; it’s possibilities and it’s risks.  There are also a large number of people that do not know about e-commerce at all.

The internet has grown by 215% in the last 7 years and even this growth through out the world encompasses only 17% of the total population.[Int] Considering the figures from [Int] the opportunity for e-commerce is astounding and at the same time the risks and destabilization factors are just as great.

Simply because we can cite a couple of companies that have survived the .com bust and prospered such as Yahoo, Google, and Amazon.com, we cannot say that e-commerce has stabilized. There is no way of knowing whether it has stabilized or not.

[Lev99] illustrates that it was the human interaction that drove the rise of civilization and eventually the internet and it is this very same force that will keep e-commerce from stabilizing completely. Some businesses will never be able to transfer all operation to e-commerce simply because of the human interaction factor that humans desire. You can send an email, but it will never be as effective as a phone conversation; while a video conference will never replace throwing back a few cold ones during a business deal. As long as every business is not able to completely operate on the internet without the bricks, e-commerce cannot be considered to be a stable operating medium for a business.

Nevertheless, e-commerce is essential for the success of modern businesses because of the pervasiveness of technology and the current drive toward automation. The internet enables e-commerce to span the globe and to give companies reach into corners of the world where access was impossible previously. To leave out e-commerce form a business model could be a devastating mistake.

E-commerce security also has a long way to go before it stabilizes. Firewalls and even biometrics can be defeated with clever exploits and social engineering opening the way for significant destabilization within e-commerce. There is nothing in ecommerce resembling the vault at Ft. Knox. Even NSA computers have been hacked and White House websites defaced. Until security on the internet is stabilized e-commerce can hardly be said to have stabilized.

[Int] internet World Stats

http://www.internetworldstats.com/stats.htm

[Lev99]Levine, Locke, Searls & Weinberger, “the cluetrain manifesto”, 1999, http://www.cluetrain.com/

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A derived metric is obtained directly from metrics in a dataset used by the document, by combining two or more existing metrics for the purpose. Derived metrics permit the dynamic application of calculations to a document without requiring new metric definitions.

For example, if your dataset contains the dollar sales for a particular region, and you want to view the same data in millions, you could create a derived metric with a definition of Dollar Sales/1,000,000.

A derived metric:
•    must be a compound metric. The reverse is not true—a compound metric does not have to be a derived metric.
•    must use metrics from the same dataset. If the new definition demands metric data not readily available, the information cannot be obtained dynamically, as the dataset must first be re-executed.

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Drill links are selectable connections from text fields or images in one document to other documents, HTML documents, or reports. Drill links can pass parameters to answer prompts in the target. When you click the object (text or image) associated with a drill link in the document, you can see its target.

A drill link contains the event to be triggered (such as executing a document or exporting a report) and the ID of the document, report, or HTML document to be executed. You could define a drill link on an attribute element in a document. When clicked, a report is executed using the attribute element in the prompt. Additionally, the drill link can pass information to the target to answer prompts in the target. This information can be one or both of the following:
•    Existing prompt answers from the source document
•    Selected attributes from the source document

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1.    Add the attribute to report.
2.    Right Click and select Remove from GRID.

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Prompt types
Prompts allow you as a user to fill in almost any part of the report definition, such as the filter or template, at the time of report execution. The report designer determines which parts of a report will be prompted at report execution and which will not. MicroStrategy Web supports the following prompt types:
•    Value prompt allows you to specify a value of any data type, such as text, numeric, or date.
•    Object prompt allows you to select a set of objects to be placed on the template (attribute, metric, consolidation, template, or custom group) or filter(s) to be used as the filter criteria in a report.
•    Attribute Element List prompt allows you to select a list of attribute elements to use as part of the filter criteria in a report.
•    Attribute Qualification prompt allows you to specify a number of attribute qualifications that become part of the filter criteria in a report.
•    Metric Qualification prompt allows you to specify a number of metric qualifications that become part of the filter criteria in a report.
•    Hierarchical Attribute prompt allows you to specify conditions based on attributes and attribute elements selected from at least one hierarchy (a combination of an attribute element list prompt and an attribute form qualification prompt) to become part of the filter criteria in a report.

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Report Filter
The Report Filter is one or several conditions applied at the time the SQL is generated to return data from the warehouse. The Report Filter can be edited only in Design Mode. In View Mode, the Report Filter can be displayed but not edited. Changing the Report Filter causes the report to re-execute and takes longer than changing the View Filter.

View Filter
The View Filter is one or several conditions that return a subset of the data in the original report. For example, if the original report has all stores in the Northeast region shown, you could choose to show Boston stores only by adding a condition to the View Filter. The View Filter can be viewed and edited in View mode; in Design Mode it can only be viewed.

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