sqlserver material 8

What is Difference between ER Modeling and Dimensional Modeling?

ER modeling is used for normalizing the OLTP database design. Dimensional modeling is used for de-normalizing the ROLAP/MOLAP design.

What is Degenerate Dimension Table?

If a table contains values, which are neither dimension nor measures, then it is called a degenerate dimension  table.

Why is Data Modeling Important?

Data modeling is probably the most labor intensive and time consuming part of the development process. The goal of the data model is to make sure that the all data objects required by the database are completely and accurately represented. Because the data model uses easily understood notations and natural language, it can be reviewed and verified as correct by the end users.
In computer science, data modeling is the process of creating a data model by applying a data model theory to create a data model instance. A data model theory is a formal data model description. In data modeling, we are structuring and organizing data. These data structures are then typically implemented in a database management system. In addition to defining and organizing the data, data modeling will impose (implicitly or explicitly) constraints or limitations on the data placed within the structure.
Managing large quantities of structured and unstructured data is a primary function of information systems. Data models describe structured data for storage in data management systems such as relational databases. They typically do not describe unstructured data, such as word processing documents, email messages, pictures, digital audio, and video. (Reference: Wikipedia)

What is a Surrogate Key?             

A surrogate key is a substitution for the natural primary key. It is just a unique identifier or number for each row that can be used for the primary key to the table. The only requirement for a surrogate primary key is that it should be unique for each row in the table. It is useful because the natural primary key can change and this makes updates more difficult. Surrogated keys are always integer or numeric.

What is Junk Dimension?

A number of very small dimensions may get lumped together to form a single dimension, i.e. a junk dimension – the attributes are not closely related. Grouping of Random flags and text Attributes in a dimension and moving them to a separate sub dimension is known as junk dimension.

What is a Data Mart?

A data mart (DM) is a specialized version of a data warehouse (DW). Like data warehouses, data marts contain a snapshot of operational data that helps business people to strategize based on analyses of past trends and experiences. The key difference is that the creation of a data mart is predicated on a specific, predefined need for a certain grouping and configuration of select data. A data mart configuration emphasizes easy access to relevant information (Reference: Wiki). Data Marts are designed to help the manager make strategic decisions about their business.

What is the Difference between OLAP and Data Warehouse?

Data Warehouse is the place where the data is stored for analysis, whereas OLAP is the process of analyzing the data, managing aggregations, partitioning information into cubes for in depth visualization.

What is a Cube and Linked Cube with Reference to Data Warehouse?

Cubes are logical representation of multidimensional data. The edge of the cube contains dimension members and the body of the cube contains data values. The linking in cube ensures that the data in the cubes remain consistent.

What is Snapshot with Reference to Data Warehouse?

You can disconnect the report from the catalog to which it is attached by saving the report with a snapshot of the data.

What is Active Data Warehousing?

An active data warehouse provides information that enables decision-makers within an organization to manage customer relationships nimbly, efficiently and proactively.

What is the Difference between Data Warehousing and Business Intelligence?

Data warehousing deals with all aspects of managing the development, implementation and operation of a data warehouse or data mart, including meta data management, data acquisition, data cleansing, data transformation, storage management, data distribution, data archiving, operational reporting, analytical reporting, security management and backup/recovery planning. Business intelligence, on the other hand, is a set of software tools that enable an organization to analyze measurable aspects of their business such as sales performance, profitability, operational efficiency, effectiveness of marketing campaigns, market penetration among certain customer groups, cost trends, anomalies and exceptions. Typically, the term ’business intelligence’ is used to encompass OLAP, data visualization, data mining and query/reporting tools. (Reference: Les Barbusinski)

What is MDS?

Master Data Services or MDS helps enterprises standardize the data people rely on to make critical business decisions. With Master Data Services, IT organizations can centrally manage critical data assets companywide and across diverse systems, enable more people to securely manage master data directly, and ensure the integrity of information over time. (Read more here)

Explain the Paradigm of Bill Inmon and Ralph Kimball.

Bill Inmon’s paradigm: Data warehouse is one part of the overall business intelligence system. An enterprise has one data warehouse, and data marts source their information from the data warehouse. In the data warehouse, information is stored in the 3rd normal form.
Ralph Kimball’s paradigm: Data warehouse is the conglomerate of all data marts within the enterprise. Information is always stored in the dimensional model.

SQL SERVER – Azure Interview Questions and Answers – Guest Post by Paras Doshi – Day 25 of 31

July 25, 2011 by pinaldave

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1.What is SQL Azure?
SQL Azure is a cloud based relational database as a Service offered by Microsoft. Conceptually it is SQL server in the cloud.
2.What is cloud computing?
National Institute of standards and computing definition of cloud computing:
Cloud computing is a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction.
[TIP: Remember Key words On Demand, Scalable, Self-service, and Measurable. Now take the first word from each key word which gives us OSSM which can be pronounced as Awesome. Thus remember cloud computing is Awesome! Tip courtesy: Dave Nielsen]
3.How is SQL Azure different than SQL server?
SQL Azure is a cloud based service and so it has own set of pros and cons when compared to SQL server. SQL Azure service benefits includes on demand provisioning, high availability, reduced management overhead and scalability. But SQL Azure abstracts some details from the subscriber which can be good or bad which depends on the context of the need.
4.How many replicas are maintained for each SQL Azure database?
For each database, three replicas are maintained for each database that one provisions. One of them is primary replica. All read/write happen on primary replica and other replicas are kept in sync with primary replica. If for some reason, primary goes down, other replica is promoted to primary. All this happens under the hood.
5.How can we migrate from SQL server to SQL Azure?
For Data Migration, we can use BCP or SSIS. And for schema Migration we can use Generate Script Wizard. Also, we could use a Tool called SQL Azure migration wizard available on codeplex.
6.Which tools are available to manage SQL Azure databases and servers?
We can manage SQL Azure database using SQL server management server 2008 R2. Also, we can manage SQL Azure databases and servers through a Silverlight app integrated in Azure management portal.
7.Tell me something about security and SQL Azure.
SQL Azure service allows blocking a request based on its IP address through SQL Azure firewall. It uses SQL server Authentication mechanism to authenticate connections. Also connections to SQL Azure are SSL-encrypted by default.
8.What is SQL Azure Firewall?
SQL Azure firewall is a security mechanism that blocks requests based on its IP address.
9.What is the difference between web edition and business edition?
SQL Azure Web edition database Max Size is 5 GB whereas the business edition supports Max Size up to 50 GB. The size of a web edition database can be increased (/decreased) in the increments (/decrements) of 1 GB whereas the size of a business edition can be increased in the increments of 10 GB.
10.How do we synchronize On Premise SQL server with SQL Azure?
We could use a No code solution called DATA SYNC (currently in community technology preview) to synchronize on-premise SQL server with SQL Azure. We can also develop custom solutions using SYNC framework.
11.How do we Backup SQL Azure Data?
SQL Azure keeps three replicas of a database to tackle hardware level issues. To tackle user level errors, we can use COPY command that allows us to create a replica of a SQL Azure database. We can also backup SQL Azure data to local SQL server using BCP, SSIS, etc. but as of now, point in time recovery is not supported.
12.What is the current pricing model of SQL Azure?
Charges for SQL Azure consumption is based on 1) Size 2) Data Transfer.
[For contemporary pricing model, read: http://www.microsoft.com/windowsazure/pricing/ ]
13.What is the current limitation of the size of SQL Azure DB?
Maximum size of a SQL Azure database is 50 GB.
14.How do you handle datasets larger than 50 GB?
As of now, we have to build custom solution at application level that can handle scale out of underlying SQL Azure databases. But Microsoft has announced, SQL Azure Federations that will assist scaling out of SQL Azure databases. And scale out means that we are splitting the data into smaller subsets spread across multiple databases.
15.What happens when the SQL Azure database reaches Max Size?
Read operations continue to work but create/insert/update operations are throttled. You can drop/delete/truncate data.
16.How many databases can we create in a single server?
150 databases (including master database) can be created in a single SQL Azure server.
17.How many servers can we create in a single subscription?
As of now, we can create six servers under a single subscription.
18.How do you improve the performance of a SQL Azure Database?
We can tune a SQL Azure database using information available from execution plan and statistics of a query. We could use SQL Azure’s Dynamic Management views to monitor and manage SQL Azure database.
Also, SQL Azure performance is affected by network latency and bandwidth. Considering this, code near application topology gives the best performance.
19.What is code near application topology?
Code near application topology means that the SQL Azure database and the windows azure hosted service consuming the data are hosted in the same Azure datacenter.
[FYI: in the code far application topology, the app connects to SQL Azure from outside the Microsoft data center]
20.What were the latest updates to SQL Azure service?
Latest SQL Azure updates include multiple servers per subscription, SQL Azure co administrator support, creating Firewall rules for servers with IP detect.
[A constantly updated list of SQL Azure features is available at http://beyondrelational.com/whatisnew/sqlserver/azure.aspx]
21.When does a workload on SQL Azure get throttled?
When database reaches its maximum size update/insert/create operations get throttled. Also there are policies in place that does not allow to a workload to exploit a shared physical server. In other words, the policies make sure that all workload get a fair share of shared physical server. Now, a workload can get soft throttled that means that the workload has crossed the safety threshold. A workload can also got hard throttled which means that a SQL Azure machine is out of resources and it does not accept new connections. We can know more about what happened by decoding reason codes.
These were SQL Azure specific interview questions but remember that SQL server specific interview questions that we have seen so far can also appear in SQL Azure context since SQL Azure is “SQL server in the cloud”. Also questions specific to supported/unsupported features can be asked. I have not included the questions specific to unsupported features because it keeps on changing. Read general guidelines and limitations. Also note that SQL Azure is evolving very fast and it is important to keep a tab on the features that are added in service releases.