Dense vs sparse indexes in DBMS Theory - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the sentence to define a dense index.

DBMS Theory

A dense index has an index record for [1] search key value in the data file.

Drag options to blanks, or click blank then click option'

Aonly one

Bsome

Cno

Devery

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'some' because sparse indexes have fewer entries.

A dense index contains an index record for every search key value in the data file, allowing direct access to each record.

2fill in blank

medium

Complete the sentence to define a sparse index.

DBMS Theory

A sparse index has index records for [1] of the search key values, typically one per data block.

Drag options to blanks, or click blank then click option'

Asome

Bnone

Chalf

Dall

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'all' because it sounds like a complete index.

A sparse index contains index records for only some of the search key values, usually one per block, reducing index size but requiring block scanning.

3fill in blank

hard

Fix the error in the statement about sparse indexes.

DBMS Theory

Sparse indexes have an index record for [1] record in the data file.

Drag options to blanks, or click blank then click option'

Ano

Bevery

Csome

Dall

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'every' because it sounds like a full index.

Sparse indexes have index records for some records, not every record, to save space.

4fill in blank

hard

Fill both blanks to complete the comparison between dense and sparse indexes.

DBMS Theory

A dense index has [1] index records, while a sparse index has [2] index records.

Drag options to blanks, or click blank then click option'

Amore

Bfewer

Cequal

Dno

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping 'more' and 'fewer'.

A dense index has more index records because it includes every search key, while a sparse index has fewer records, indexing only some keys.

5fill in blank

hard

Fill all three blanks to complete the explanation of index usage.

DBMS Theory

Dense indexes provide [1] access but [2] storage space, while sparse indexes provide [3] access but save storage space.

Drag options to blanks, or click blank then click option'

Afast

Bmore

Cslower

Dless

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up 'fast' and 'slower' or 'more' and 'less'.

Dense indexes provide fast access because every key is indexed, but they use more storage space. Sparse indexes save storage space but access can be slower because not every key is indexed.

Practice

1. What is the main difference between a dense index and a sparse index in a database?

easy

A. Dense index stores data physically; sparse index stores data logically.

B. Sparse index has an entry for every record; dense index has entries for some records only.

C. Dense index has an entry for every record; sparse index has entries for some records only.

D. Sparse index is faster than dense index in all cases.

Solution

1. Step 1: Understand dense index definition

   A dense index contains an index entry for every record in the data file, making lookups very fast.

2. Step 2: Understand sparse index definition

   A sparse index contains entries only for some records, usually one per data block, saving space but requiring extra searching inside blocks.

3. Final Answer:

   Dense index has an entry for every record; sparse index has entries for some records only. -> Option C

4. Quick Check:

   Dense = every record, Sparse = some records [OK]

Hint: Dense = all entries, sparse = fewer entries [OK]

Common Mistakes:

• Confusing which index has entries for every record
• Thinking sparse index is always faster
• Assuming dense index saves more space

2. Which of the following is the correct syntax to describe a sparse index in a database textbook?

easy

A. "An index with entries for every record in the data file."

B. "An index that duplicates all data entries."

C. "An index that stores the entire data file."

D. "An index with entries only for some records, typically one per block."

Solution

1. Step 1: Recall sparse index definition

   Sparse index contains entries only for some records, usually one per block, to save space.

2. Step 2: Match options with definition

   "An index with entries only for some records, typically one per block." correctly describes sparse index as having entries only for some records.

3. Final Answer:

   "An index with entries only for some records, typically one per block." -> Option D

4. Quick Check:

   Sparse index = fewer entries per block [OK]

Hint: Sparse index = fewer entries, usually one per block [OK]

Common Mistakes:

• Choosing dense index description for sparse index
• Confusing sparse index with full data storage
• Selecting options that describe dense index

3. Consider a database with 1000 records stored in 100 blocks. If a sparse index has one entry per block, how many entries does the sparse index have?

medium

A. 100

B. 1000

C. 10

D. 1

Solution

1. Step 1: Understand sparse index entry count

   Sparse index has one entry per block, not per record.

2. Step 2: Calculate entries based on blocks

   Given 100 blocks, sparse index will have 100 entries.

3. Final Answer:

   100 -> Option A

4. Quick Check:

   Entries = blocks = 100 [OK]

Hint: Sparse index entries = number of blocks [OK]

Common Mistakes:

• Confusing entries with total records
• Assuming sparse index has one entry per record
• Choosing a number unrelated to blocks

4. A database administrator created an index with entries for every record but calls it a sparse index. What is the error in this scenario?

medium

A. The index is actually a dense index, not sparse.

B. Sparse index must have entries for every record.

C. Sparse index stores data physically, not index entries.

D. There is no error; this is a valid sparse index.

Solution

1. Step 1: Identify index type by entry count

   An index with entries for every record is a dense index by definition.

2. Step 2: Understand sparse index definition

   Sparse index has fewer entries, not one per record.

3. Final Answer:

   The index is actually a dense index, not sparse. -> Option A

4. Quick Check:

   Entries per record = dense, not sparse [OK]

Hint: Entries for every record means dense index [OK]

Common Mistakes:

• Thinking sparse index can have all entries
• Confusing physical data storage with index entries
• Believing no error exists in naming

5. You have a large database where fast search is critical, but storage space is limited. Which index type should you choose and why?

hard

A. Sparse index, because it uses less space and is always faster.

B. Dense index, because it provides faster search at the cost of more space.

C. Dense index, because it uses less space and slower search.

D. Sparse index, because it provides faster search and uses more space.

Solution

1. Step 1: Analyze speed vs space trade-off

   Dense index has an entry for every record, making search very fast but uses more space.

2. Step 2: Match requirement with index type

   Since fast search is critical, dense index is preferred despite higher space usage.

3. Final Answer:

   Dense index, because it provides faster search at the cost of more space. -> Option B

4. Quick Check:

   Fast search needs dense index [OK]

Hint: Fast search needs dense index, space saving needs sparse [OK]

Common Mistakes:

• Choosing sparse index for fastest search
• Confusing space usage of dense vs sparse
• Ignoring trade-offs between speed and storage