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Data Modeling Interview Questions & Answers - Learning Mode
COOLINTERVIEW.COM CONCEPTS AND ARCHITECTURE INTERVIEW QUESTIONS DATA MODELING INTERVIEW QUESTIONS QUESTIONS & ANSWERS - LEARNING MODE

Data Modeling Interview Questions & Answers - Learning Mode

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. Data modeling is often the first step in database design and object-oriented programming as the designers first create a conceptual model of how data items relate to each other. Data modeling involves a progression from conceptual model to logical model to physical schema.

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Data Modeling Interview Questions & Answers - Learning Mode
Try Data Modeling Interview Questions & Answers - Exam Mode
Question: What is the difference between star flake and snow flake schema?



Answer: Star Schema:

Well in star schema you just enter your desired facts and all the primary keys of your dimensional tables in Fact table. And fact tables primary is the union of its all dimension table key. In star schema dimensional tables are usually not in BCNF form.

SnowFlake:

Its almost like starschema but in this our dimension tables are in 3rd NF, so more dimensions tables. And these dimension tables are linked by primary, foreign key relation.
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Question: When should you consider denormalization?



Answer: Denormalization is used when there is a lot of tables involved in retreiving data.Denormalization is done in dimentional modelling used to construct a data ware house.This is not usually done for data bases of transactional systems.

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Question: What is the difference between hashed file stage and sequential file stage in relates to DataStage Server



Answer: In datastage server jobs,can we use sequential filestage for a lookup instead of hashed filestage.If yes ,then whats the advantage of a Hashed File stage over sequential filestage

search is faster in hash files as you can directly get the address of record directly by hash algorithm as records are stored like that but in case of sequential file u must compare all the records.

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Question: What is data sparsity and how it effect on aggregation?



Answer: Data sparsity is term used for how much data we have for a particular dimension/entity of the model.

It affects aggregation depending on how deep the combination of members of the sparse dimension make up. If the combination is a lot and those combinations do not have any factual data then creating space to store those aggregations will be a waste as a result, the database will become huge.
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Question: Why are recursive relationships are bad? How do you resolve them?



Answer: Recursive relationships are an interesting and more complex concept than the relationships you have seen in the previous chapters, such as a one-to-one, one-to-many, and many-to-many. A recursive relationship occurs when there is a relationship between an entity and itself. For example, a one-to-many recursive relationship occurs when an employee is the manager of other employeess. The employee entity is related to itself, and there is a one-to-many relationship between one employee (the manager Source: CoolInterview.com
Question: Describe the third normal form

Answer: An entity is in the third normal form if it is in the second normal form and all of its attributes are not transitively dependent on the primary key. Transitive dependence means that descriptor key attributes depend not only on the whole primary key, but also on other descriptor key attributes that, in turn, depend on the primary key. In SQL terms, the third normal form means that no column within a table is dependent on a descriptor column that, in turn, depends on the primary key.

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Question: What is an artificial (derived) primary key? When should it be used?



Answer: Using a name as the primary key violates the principle of stability. The social security number might be a valid choice, but a foreign employee might not have a social security number. This is a case where a derived, rather than a natural, primary key is appropriate. A derived key is an artificial key that you create. A natural key is one that is already part of the database. Source: CoolInterview.com
Question: What is ERD?



Answer: Data models are tools used in analysis to describe the data requirements and assumptions in the system from a top-down perspective. They also set the stage for the design of databases later on in the SDLC.

There are three basic elements in ER models:
Entities are the "things" about which we seek information.
Attributes are the data we collect about the entities.
Relationships provide the structure needed to draw information from multiple entities Source: CoolInterview.com
Question: Is this statement TRUE or FALSE ? all databases must be in third normal form?



Answer: In general all organization data bases are normalised to 3nf inorder to remove redundancy and efficent access.A data base can also be created with out normalisation.Hence it is not a mandatory that a database should be in 3nf.

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Question: What is First Normal Form



Answer: First Normal Form (1NF)

A table satisfying the properties of a relation is said to be in first normal form. As discussed in an earlier chapter, a relation cannot have multivalued or composite attributes. This is what the 1NF requires.

A relation is in 1NF if and only if all underlying domains contain atomic values only.

The first normal form deals only with the basic structure of the relation and does not resolve the problems of redundant information or the anomalie Source: CoolInterview.com
Question: Waht is second normal form



Answer: An entity is in the second normal form if all of its attributes depend on the whole (primary) key. In relational terms, every column in a table must be functionally dependent on the whole primary key of that table. Functional dependency indicates that a link exists between the values in two different columns.

If the value of an attribute depends on a column, the value of the attribute must change if the value in the column changes. The attribute is a function of the column. The followin Source: CoolInterview.com

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Latest 20 Questions
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