Fix spelling mistakes

1 files changed, 18 insertions, 18 deletions

diff --git a/doc/unit-4.md b/doc/unit-4.md
index b5bd1ba..5ba9826 100644
--- a/doc/unit-4.md
+++ b/doc/unit-4.md
@@ -12,6 +12,7 @@
     * their fields
 
 Read: Chapter 5
+
 * the physical database design process
 * designing fields
 * denormalizing and partitioning data
@@ -48,13 +49,13 @@ Important terms:
 
 #### Designing Fields
 
-> Field: The smallest unit of application data reconized by system software.
+> Field: The smallest unit of application data recognized by system software.
 
 * type of data
 * data integrity controls
 * handling of missing values for the field
 
-> data type: a detailed coding scheme recognized by software system for representing organizational data.
+> data type: a detailed coding scheme recognized by software systems for representing organizational data.
 
 * space to store data
 * speed required to access data
@@ -103,7 +104,7 @@ Important terms:
 
 ### Denormalizing
 
-noramlized relations solve maintenance anomolies and
+normalized relations solve maintenance anomalies and
 minimize redundancies. This may not yield efficient data processing
 if the data required is across many relations. i.e JOINS are costly
 if the data isn't near each other.
@@ -120,7 +121,7 @@ Opportunities for denormalization
 Dangers of denorm
 
 * increase chance of errors and inconsistencies
-* optimization for one type of processing make affect a different type of processing
+* optimization for one type of processing may affect a different type of processing
 * more storage space requirements
 
 ### Partitioning
@@ -134,7 +135,7 @@ Partition key
 * single column
 * date: usually a qualifier in queries
 
-Makes table maintainenance easier because fragementing and rebuliding can be isolated to single partitions
+Makes table maintenance easier because fragmenting and rebuilding can be isolated to single partitions
 as storage space needs to be organized.
 
 File level security can be applied to prohibit users from seeing certain rows of data.
@@ -144,7 +145,6 @@ still allows processing against the other partitioned files to continue.
 Each partitioned file can be placed on a separate disk drive to reduce contention for the same drive
 and hence improve query and maintenance performance across the database.
 
-
 Horizontal partitioning is similar to creating supertype/subtype relationship because different types
 of the entity are involved in different relationships.
 
@@ -168,7 +168,7 @@ Range partitioning
 * A table row is inserted in the proper partition based on it's initial values for the range fields.
 * Each partition may hold a different number of rows.
 * A partition key that can produce a more balanced distribution of rows is better.
-* A row may be restricted fro moving between partitions when key values are updated.
+* A row may be restricted from moving between partitions when key values are updated.
 
 Hash Partitioning
 
@@ -210,7 +210,7 @@ Read:
 
 > physical file: a named portion of secondary memory (hdd) allocated for the purpose of storing physical records.
 
-> tablespace: a named logical storage unit in which data fro one or more database tables, views or other database objects may be stored.
+> tablespace: a named logical storage unit in which data from one or more database tables, views or other database objects may be stored.
 
 > extent: a contiguous section of disk storage space.
 
@@ -231,7 +231,7 @@ Not used in databases due to their inflexibility, but may be used for backups.
 
 Indexed File Organization
 
-The records are stored sequentially or nonsequentially and an index is created that allows the
+The records are stored sequentially or non-sequentially and an index is created that allows the
 application software to locate individual records.
 
 > Index: is a table that is used to determine in a file the location of records that satisfy some condition.
@@ -239,7 +239,7 @@ application software to locate individual records.
 Each index entry matches a key value with one or more records.
 An index that allows each entry to point to more than one record is called a secondary key index.
 
-> Secondary key: one field or a combination of fields for which more than one record may have the same combination of values. Also called a nonunique key.
+> Secondary key: one field or a combination of fields for which more than one record may have the same combination of values. Also called a non-unique key.
 
 > join index: An index on columns from two or more tables that come from the same domain of values.
 
@@ -256,7 +256,7 @@ Typical hashing algorithm uses the technique of dividing each primary key value
 > Pointer: a field of data indicating a target address that can be used to locate related field or record of data.
 
 * an index table is smaller than a data table.
-* added expense of storing and maintaining the index space.
+* Added expense of storing and maintaining the index space.
 
 File organization overview
 
@@ -278,12 +278,12 @@ File organization overview
   * hashed: not possible unless using hash index
 * deleting records:
   * sequential: can create wasted space or require reorganizing
-  * indexed: if space can be dynamically allocated, easy. requires maintenance of indexes
+  * indexed: if space can be dynamically allocated, easy. Requires maintenance of indexes
   * hashed: very eash
 * adding new records:
   * sequential: requires rewriting a file
-  * indexed: if space can be dynamically allocated, easy. requires maintenance of indexes.
-  * hashed: very easy. hash collisions need extra work.
+  * indexed: if space can be dynamically allocated, easy. Requires maintenance of indexes.
+  * hashed: very easy. Hash collisions need extra work.
 * updating records:
   * sequential: usually requires rewriting a file
   * indexed: easy but requires maintenance of indexes
@@ -315,7 +315,7 @@ CREATE INDEX products_fk ON orders(product_id);
 
 When to use indexes
 
-There is a tradeoff between improved read performance and degraded write performance due to 
+There is a trade-off between improved read performance and degraded write performance due to 
 index maintenance.
 
 Indexes can be used generously for systems that are read heavy but beware in systems that
@@ -331,7 +331,7 @@ Guidelines:
 6. Indexes on large values is not optimal. Try to find a smaller coded value to index to represent the larger value.
 7. If the key for the index is used to determine the location where the record will be stored then a surrogate key should be used.
 8. Check DBMS for limits on the # of indexes on a table. (limits include # of indexes, and size of index)
-9. Be careful of indexing attributes that have null values. some systems don't index `null` so sequential scan is needed for `null` value.
+9. Be careful of indexing attributes that have null values. Some systems don't index `null` so sequential scan is needed for `null` value.
 
 ### Designing a database for optimal query performance
 
@@ -341,8 +341,8 @@ Parallel query processing
 
 ## Summary
 
-denormalization transforms normalized relations into non-normalized implementations specs.
-Horizontal paritioning breaks a relation into multiple record specifications by placing different
+De-normalization transforms normalized relations into non-normalized implementations specs.
+Horizontal partitioning breaks a relation into multiple record specifications by placing different
 rows into different tables, based on common column values.
 Vertical partitioning distributes the columns of a relation into separate files, repeating the primary key in each of the files.