Question: Which 16-book novel series created by Deborah Gregory in 1999 was adapted both to a film and then a television series in 2003?
Context: Shigofumi: Letters from the Departed, titled Shigofumi: Stories of Last Letter (シゴフミ ～Stories of Last Letter～ ) in Japan, or simply Shigofumi, is a Japanese anime television series created by Tomorō Yuzawa and produced by Bandai Visual and Genco, which aired in Japan on Chiba TV and other networks between January 6 and March 22, 2008 and contains twelve episodes.  An original video animation episodes was included with the final anime DVD volume released on September 26, 2008.  A light novel series was originally adapted from the anime's premise set by Tomorō Yuzawa, featuring story composition and illustrations by Ryō Amamiya and Poko, respectively.  Four novels were published by MediaWorks under their "Dengeki Bunko" imprint between October 2006 and March 2008.  Despite the novels being produced first, the anime is considered the original work, as stated by Yuzawa.  The anime has been acquired by Bandai Visual for English language localization.  The title "Shigofumi" comes from the combination of the Japanese words for "after death" (死後 , shigo ) , and "letter" (文 , fumi ) , which literally translates to an "after death letter". The "Monogatari" Japanese anime television series is based on the light novel series of the same name, written by Nisio Isin with illustrations by Vofan.  The anime is directed by Akiyuki Shinbō and produced by the animation studio Shaft.  The series debuted with "Bakemonogatari" and aired 12 episodes between July 3 and September 25, 2009, on the Tokyo MX television station.  Three additional original net animation episodes were distributed on the anime's official website between November 3, 2009, and June 25, 2010.  A sequel titled "Nisemonogatari" aired 11 episodes between January 7 and March 17, 2012.  A prequel to the original series titled "Nekomonogatari (Black)" aired four episodes back-to-back on December 31, 2012.  Six further sequels were later adapted under the common moniker of "Monogatari Series Second Season": "Nekomonogatari (White)", "Kabukimonogatari", "Otorimonogatari", "Onimonogatari" and "Koimonogatari" aired between July 6 and December 28, 2013, whereas "Hanamonogatari", which was originally meant to air with the others in 2013, was postponed and eventually broadcast separately on August 16, 2014.  The first novel of the "final season" was adapted as "Tsukimonogatari", which aired on December 31, 2014. Ojamajo Doremi (おジャ魔女どれみ , lit.  "Bothersome Witch Doremi") , also known as Magical DoReMi in some countries, is a Japanese magical girl anime television series created by Toei Animation.  It focuses on a group of elementary school girls, led by Doremi Harukaze, who become witch apprentices.  The series aired in Japan on TV Asahi between February 1999 and January 2003, spanning four seasons and 201 episodes, and was followed by an original video animation series released between June and December 2004.  An English language version of the first season, produced by 4Kids Entertainment, aired in North America in 2005.  The franchise has also spawned two companion films, various manga adaptations, and a sequel light novel series. The Cheetah Girls is a 16-book novel series created and written by Deborah Gregory.  The series, which began in 1999, is about a female vocal group seeking success and fortune.  In the book series, there are five Cheetah Girls, but in the first film adaption and its sequel, there are only four.  In the , there are only three. Gokudo-kun the Adventurer (ゴクドーくん漫遊記 , Gokudō-kun Man'yūki ) is a fantasy light novel series created by Usagi Nakamura.  The light novel was first serialized by Kadokawa Shoten in their light novel magazine Kadokawa Sneaker Bunko.  It was later adapted into a manga in 1995 and is released in Dengeki Daioh magazine.  An anime adaptation is then produced by Trans Arts and was aired TV Tokyo from April 2, 1999 to September 24, 1999, with a total of 26 episodes. The Cheetah Girls is a 2003 television film based on the book series of the same name by Deborah Gregory. Yume no Crayon Oukoku (夢のクレヨン王国 , Yume no Kureyon Ōkoku , lit.  "The Crayon Kingdom of Dreams") is a seventy-episode anime television series created by Toei Animation and broadcast from 1997 to 1999.  It was based on the novel series by Reizo Fukunaga, and was adapted into a manga by Michiru Kataoka and serialized in "Nakayoshi" from 1997 to 1998.  It has been dubbed into French, Italian, Korean and Chinese.  The original features the voice talents of Yuka Tokumitsu as Princess Silver. Deborah Gregory is the author of the popular book series "The Cheetah Girls".  She was also the co-producer of the Disney Channel Original Movies "The Cheetah Girls" and "The Cheetah Girls 2", as well as an executive producer for "". The Legend of Chu Liuxiang is a Chinese television series directed by Aman Chang, starring Taiwanese actor-singer Ken Chang as the protagonist Chu Liuxiang from the "wuxia" novel series "Chu Liuxiang Series" by Gu Long.  The series is adapted from four novels in the "Chu Liuxiang Xinzhuan" segment of the novel series.  Filming for the series started in October 2010 in the Water Margin Film City in Dongping County, Shandong Province, China.  It was first broadcast on ChingTV in South Korea on 14 June 2012. Brothers Conflict (ブラザーズ コンフリクト , Burazāzu Konfurikuto ) , also known as BroCon, is a Japanese novel series created by Atsuko Kanase, written by Takeshi Mizuno and illustrated by Udajo.  It has been adapted into two PlayStation Portable video games by Idea Factory, a yonkoma manga series and an anime television series.  The 12-episode anime aired between July and September 2013.  It is animated by Brain's Base.  Funimation acquired the North American streaming rights for the anime.  Funimation released a "The Complete Series + OVA - Limited Edition Blu-ray & DVD" on March 8, 2016.
Answer: The Cheetah Girls